
What's in this deep dive
- What a Treasury bill actually is
- Sold at a discount, redeemed at par
- Why there is no coupon to reinvest
- The terms on offer and what each one suits
- A worked bill from purchase to maturity
- The two rates quoted on the same bill
- How the discount rate is computed
- How the investment rate is computed
- The comparison error that decides the wrong way
- From investment rate to an APY equivalent
- Where the missing points actually live
- State and local tax, the part that is genuinely a feature
- Working the taxable equivalent yield
- What federal tax does to the picture
- Buying at auction
- Competitive versus non-competitive bidding
- Buying on the secondary market instead
- Holding to maturity against selling early
- How far rates would have to move to hurt you
- Rolling bills instead of building a ladder
- Bills against a high-yield savings account
- Bills against a money market fund
- What bills are not good for
- Common mistakes with Treasury bills
- The bottom line
A Treasury bill is the instrument most people reach for when they have money that is not really investment capital: a house deposit two seasons out, a tax bill coming due, a cash reserve that has grown past the point where a savings rate feels like enough. Our explainer on how bonds work covers the long end of that family, and our note on what a bond ladder is covers how to arrange several maturities at once. The bill is the short end, and it behaves differently enough from a coupon bond that most of the intuition people bring to it is slightly wrong.
This explainer covers what a bill is, the discount mechanism that separates it from every coupon-paying bond, the terms on offer and what each one suits, and the single most consequential piece of arithmetic in the whole subject: the fact that the same bill is quoted with two different rates, and that comparing the wrong one against a savings APY reliably produces the wrong decision. It then works the state and local tax exemption properly, covers auctions and secondary purchases, shows exactly how far rates would have to move before selling early cost you anything, and sets bills honestly beside savings accounts and money market funds. Run your own numbers in the companion below or in our calculator as you read. Every rate and dollar figure here is illustrative arithmetic, education rather than advice.
Key takeaways
- A Treasury bill pays no interest along the way. You buy below face value and receive face value at maturity, and the gap between the two is the entire return, which makes it a zero-coupon instrument with nothing to reinvest mid-term.
- The same bill is quoted with two different rates. On the illustrative 182-day bill used throughout, the discount rate is 4.00 percent and the investment rate is 4.14 percent, and only the second belongs in a comparison against a savings APY.
- Interest on Treasury securities is generally exempt from state and local income tax. For a reader facing an illustrative 6 percent state and local marginal rate, an effective 4.18 percent bill matches a fully taxable 4.45 percent, a gap of 0.45 points over the quoted headline.
- Price risk exists only if you sell early, and short bills are forgiving. On the illustrative bill, sold at the halfway point, rates would have to double before the sale returned less than the purchase price.
- Bills, savings accounts and money market funds trade off rate certainty, same-day access and effort in different proportions. Every figure in this explainer is illustrative and none describes any current market.
What a Treasury bill actually is
A Treasury bill is a short-term debt security issued by the national government, with an original term of one year or less. You lend the government money now, and the government repays a fixed, known amount on a fixed, known date. That is the whole contract. There is no periodic payment, no variable rate, no call feature, and nothing about the arrangement that changes after you buy it.
What distinguishes bills from the rest of the government debt family is only the term. The same issuer sells notes with terms of a few years and bonds with terms measured in decades, and those pay interest twice a year in the ordinary way. Bills sit at the short end and are structured differently, which is the part worth understanding rather than memorizing.
The credit question, which dominates any discussion of corporate bonds, is close to absent here. A bill is an obligation of the national government, backed by its full faith and credit, which is conventionally treated as the reference point against which other credit risk is measured. That does not make a bill risk-free in every sense, since inflation and reinvestment risk both survive, but the specific worry that the borrower fails to pay is the smallest one in the room.
Sold at a discount, redeemed at par
Here is the mechanism, and it is the single thing to hold onto. A bill has a face value, sometimes called par, which is what the government pays you on the maturity date. You do not pay face value to buy it. You pay less, and the difference between what you pay and what you receive is your return.
Work an illustrative case. A 26-week bill with a face value of $10,000, quoted at a discount rate of 4.00 percent, prices at $9,797.78. On the maturity date, 182 days later, the government pays $10,000. Your return is $202.22. No cheque arrived in between, no rate changed, and nothing about the outcome depended on what markets did during those 182 days.
That is the discount mechanism. It is not a trick or a quirk of accounting; it is a genuinely different way of packaging the same economic transaction. A coupon bond hands you a slice of the return periodically and returns your principal at the end. A bill withholds every penny of the return until the end and then pays it all at once, folded into the redemption. The economics rhyme. The cash flows do not, and the difference matters more than it looks.
Why there is no coupon to reinvest
Because a bill makes no payments before maturity, it has no reinvestment problem inside its own life. A five-year coupon bond paying twice a year throws off ten payments, and every one of them lands in your account at whatever rate then prevails and has to be redeployed. Those ten small decisions are why the yield a coupon bond actually delivers over its life is never quite the yield printed at purchase.
A bill has none of that. There is one purchase and one redemption. Whatever return the arithmetic promised at purchase is exactly what you receive, provided you hold to maturity, because there is no intermediate cash flow to be reinvested at the wrong moment. That property is worth more than most beginners realize, and it is why bills are the cleanest instrument in the entire fixed income family for teaching purposes.
The reinvestment problem does not disappear. It moves. Instead of ten small decisions spread across five years, you get one large decision on a single date: what to do with the full face value when it lands. That concentration is the real trade, and it is exactly the problem that a ladder, or a rolling programme of bills, exists to break up again. Our explainer on dividends against interest covers why the two income shapes behave so differently in a portfolio.
The terms on offer and what each one suits
Bills are issued in a small set of standard terms rather than in whatever length you fancy. In recent years the standard set has run from four weeks out to 52 weeks, with several regular steps in between, and the shortest terms come to auction far more often than the longest. Because issuance calendars are revised from time to time, confirm the current list of terms and auction dates with the Treasury’s own material rather than with any article.
The choice of term is a choice about two things at once: how long you are prepared to have the money committed, and how long you want the rate locked. Those pull in opposite directions. A four-week bill gives your money back almost immediately and locks essentially nothing; a 52-week bill locks a rate for a full year and puts the money out of reach for that year unless you sell.
At a single discount rate, the dollar return scales almost exactly with the number of days you are committed, which makes the trade-off unusually easy to see.
Dollar return per $10,000 of face value, by bill term
Illustrative arithmetic holding the quoted discount rate constant at 4.00 percent across every term, which real markets do not do. Return equals face value multiplied by the discount rate multiplied by days divided by 360. Bar widths scale to the largest figure.
Illustrative only. Holding the rate flat across terms is a teaching simplification: in practice each term carries its own rate and the longer ones do not always pay more. What the chart does show honestly is that at any single rate the dollar return is proportional to days committed, so a 26-week bill returns exactly twice a 13-week one.
A worked bill from purchase to maturity
Take the 26-week bill and follow it end to end, because every figure in the rest of this explainer traces back to this one transaction. Face value $10,000. Term 182 days. Quoted discount rate 4.00 percent, an illustrative figure chosen for clean arithmetic and not a quote of anything.
The price is face value less the discount, and the discount is face value multiplied by the rate multiplied by the fraction of a 360-day year. That is $10,000 multiplied by 0.04 multiplied by 182 divided by 360, which is $202.22. Subtract it and the price is $9,797.78. That is the cash that leaves your account on settlement day.
On day 182 the government pays $10,000. Your account is $202.22 better off than the $9,797.78 you committed. Nothing else happened in between. If you want the same walk-through on your own numbers, the companion above recalculates every figure from a face value, a rate and a day count, and our calculator sits alongside it for the longer-horizon question of what any of this is ultimately funding.
Hold those four numbers: $10,000 face, $9,797.78 price, $202.22 return, 182 days. Everything that follows is a different way of describing them.
The two rates quoted on the same bill
Now the part that decides most real comparisons and that almost nobody is told. The transaction above has one dollar return, $202.22, and two standard ways of expressing it as an annual percentage. Both are published. Both are correct within their own convention. They are different numbers, and picking the wrong one is the classic error in this whole subject.
The first is the discount rate, sometimes called the bank discount yield. It is the figure the auction announces and the figure most quoting screens lead with. On our bill it is 4.00 percent, which is where the price came from in the first place.
The second is the investment rate, also published as the coupon equivalent or the bond equivalent yield. On the identical bill it is 4.14 percent. Same bill, same $202.22, same 182 days, and a number that is 0.14 percentage points higher. Neither is a mistake or a marketing figure. They differ because they divide by different denominators and annualize on different year lengths, and the next two sections take each apart.
How the discount rate is computed
The discount rate takes the dollar return and divides it by the face value, then annualizes it by scaling to a 360-day year. Written out: return divided by face value, multiplied by 360, divided by days. On our bill that is $202.22 divided by $10,000, which is 2.0222 percent, multiplied by 360 divided by 182, which gives 4.00 percent.
Two conventions in that formula are doing quiet damage. The first is dividing by face value rather than by price. You did not invest $10,000; you invested $9,797.78. Dividing a return by a number larger than what you committed produces a percentage smaller than the return you actually earned on your money.
The second is the 360-day year. A 360-day year is a money-market convention with a long history and no particular claim to accuracy. Annualizing over 360 days when there are 365 in a year understates a genuinely annual figure slightly. Both conventions push in the same direction, which is why the discount rate is always the lower of the two published numbers on any bill. It is the right number for pricing the bill and the wrong number for deciding where your cash should live.
How the investment rate is computed
The investment rate fixes both conventions. It divides the return by the price you actually paid, and it annualizes on a 365-day year. Written out for a bill of half a year or less: return divided by price, multiplied by 365, divided by days.
On our bill that is $202.22 divided by $9,797.78, which is 2.0640 percent for the 182-day period, multiplied by 365 divided by 182, which is 4.14 percent. The same answer comes from the shorthand the Treasury publishes for short bills: 365 multiplied by the discount rate, divided by the quantity 360 minus the discount rate multiplied by days. That is 14.6 divided by 352.72, which is 4.14 percent.
One caution, because it catches people out. For bills with terms longer than about half a year, a 52-week bill in particular, the investment rate formula changes shape, because more than one semiannual compounding period is involved and the calculation has to account for it. Do not annualize a 52-week bill with the simple arithmetic above and assume you have the published figure. Read the investment rate the auction reports rather than deriving your own.
The comparison error that decides the wrong way
Here is the error in its natural habitat. A reader sees a bill quoted at 4.00 percent. They see a savings account advertising 4.05 percent APY. They conclude, reasonably enough, that the savings account pays more and is also more convenient, and they leave the money where it is.
Every step of that reasoning is defensible and the conclusion is wrong, because 4.00 percent and 4.05 percent are not the same kind of number. The 4.00 percent is a discount rate on a 360-day year divided by face value. The 4.05 percent is an annual percentage yield: return divided by the money actually committed, on a 365-day year, with compounding included. Comparing them is comparing a measurement in one unit against a measurement in another.
Convert the bill onto the savings account’s own basis and the ranking flips before tax is even mentioned. The bill’s investment rate is 4.14 percent, already ahead of 4.05 percent, and the investment rate is still not quite an APY because it does not include compounding. The next section closes that last gap. The habit worth building is simple: never compare a quoted discount rate against anything. Convert first, then compare.
From investment rate to an APY equivalent
An APY is an effective annual yield. It answers the question of what a rate compounds to over a full year, which is why two accounts paying the same nominal rate on different compounding schedules advertise different APYs. Our note on simple against compound interest works that distinction in detail.
The investment rate is a simple annualization. It scales a 182-day return up to a year by multiplying, not by compounding. To put a bill onto a true APY footing you have to ask what happens if the 182-day return is earned, then earned again on the larger balance for the remainder of the year.
On our bill the period return is 2.0640 percent over 182 days. Compounding that for 365 divided by 182 periods gives an effective annual yield of 4.18 percent. So the same bill carries three legitimate numbers: a 4.00 percent discount rate, a 4.14 percent investment rate, and a 4.18 percent effective annual yield. The last one is the number that stands beside a 4.05 percent APY on equal terms, and it beats it by 0.13 points before a word has been said about tax. Note the honest caveat: that compounding assumes you can reinvest the proceeds at a similar rate when the bill matures, which is a real assumption and not a guarantee.
Where the missing points actually live
Set the two ends of that chain side by side. The headline says 4.00 percent. The fully comparable, after-conversion, after-tax-adjusted figure for an illustrative reader facing a 6 percent combined state and local marginal rate is 4.45 percent, and the next two sections derive that. The quoted number understates the comparable one by 0.45 percentage points, which on an illustrative $9,797.78 committed for half a year is a real amount of money.
Those 0.45 points are not one adjustment. They are three, and they are wildly unequal in size.
What the quoted 4.00 percent leaves out, adjustment by adjustment
The 0.45 percentage points between the quoted discount rate and the fully comparable taxable-equivalent yield, on the illustrative 182-day bill and a 6 percent combined state and local marginal rate. Segments sum to 100.
Illustrative only. Moving from the discount rate to the investment rate adds 0.14 points, compounding to an effective annual basis adds 0.04, and the state and local tax exemption at a 6 percent rate adds 0.27, for 0.45 in total. The tax exemption is the largest single piece and the one most often left out of the comparison entirely.
The proportions are worth staring at. The conversion arithmetic that this explainer has spent three sections on accounts for roughly two fifths of the gap. The tax treatment, which takes one line to state, accounts for the other three fifths. Both matter, and the one people skip is the bigger one.
State and local tax, the part that is genuinely a feature
As a general rule, interest on Treasury securities is subject to federal income tax and exempt from state and local income taxes. That is not a loophole or a temporary provision; it is a long-standing feature of how these securities are treated, and it applies to bills in the same way it applies to notes and bonds.
For a reader in a state with no income tax, this changes nothing at all and can be ignored. For a reader facing a meaningful combined state and city rate, it is the single largest factor in the comparison against a bank account, and it is almost never mentioned in the same breath as the rate. A savings account’s interest is generally taxable at every level that taxes income. A bill’s is not taxable at the state or local level.
The size of the benefit scales directly with your own marginal rate, which means there is no universal answer and no figure an article can hand you. It also means the comparison genuinely differs from reader to reader: two people looking at the identical bill and the identical savings account can correctly reach opposite conclusions. Tax rules change and vary by jurisdiction, so treat everything here as the general principle and confirm your own position with a qualified tax professional.
Working the taxable equivalent yield
The arithmetic is one division. A taxable-equivalent yield asks what a fully taxable instrument would have to pay to leave you with the same money after tax. Take the exempt yield and divide it by one minus your marginal rate.
On our bill, the effective annual yield is 4.18 percent and the illustrative combined state and local marginal rate is 6 percent. That is 4.18 divided by 0.94, which is 4.45 percent. A savings account would have to advertise 4.45 percent APY to match, after state tax, a bill quoted at 4.00 percent. Against the 4.05 percent account from earlier, the bill is not narrowly ahead; it is ahead by 0.40 points.
Run the same division at other rates to see the shape. At a 3 percent marginal rate the bill is worth 4.31 percent. At 5 percent, 4.40 percent. At 9 percent, 4.60 percent. At 10 percent, 4.65 percent. And at zero, it is worth exactly its 4.18 percent and no more. In dollars on the illustrative $9,797.78 committed for 182 days, the bill returns $202.22 while the 4.05 percent savings account returns about $195.89 before tax and about $184.13 after a 6 percent state rate, an edge of roughly $18 for half a year on under ten thousand dollars.
What federal tax does to the picture
Federal tax is owed on a bill’s return, generally as ordinary interest income rather than at any preferential rate. That is the same treatment savings interest typically receives, which is what makes the comparison above hold up: federal tax applies to both sides at the same rate and therefore cancels out of the ranking, even though it reduces both figures.
The $18 edge computed above is a pre-federal-tax number, and the after-federal-tax edge is smaller in proportion to your federal bracket. What does not change is the direction. If two instruments face identical federal treatment and only one of them also faces state tax, the exempt one wins on any positive state rate, and the size of the win is set by that rate alone.
Timing is the detail worth flagging. For a bill held to maturity, the return is generally recognized when the bill matures rather than accrued month by month, which for a bill bought in one tax year and maturing in the next can shift the income into the later year. That mechanism has conditions and exceptions attached to it, and the treatment of a bill sold before maturity differs again. This is exactly the sort of question to put to a qualified tax professional rather than to an article, and the relevant tax authority publishes its own material on it.
Buying at auction
Bills come into existence at auction. The government announces the term and the amount it intends to sell, bids are submitted by a deadline, the auction clears at a single rate, and every successful bidder receives bills at that same rate. Shorter terms come to auction frequently, longer ones less often, and the calendar is published in advance.
Two routes exist for an ordinary saver. The first is buying directly through the government’s own purchase system, which is designed for exactly this and typically carries no commission. Bills there are commonly available with a $100 minimum in $100 increments, though minimums and increments are administrative details worth confirming rather than assuming. The second is placing an auction order through a brokerage, which passes your bid into the same auction and may or may not charge for the service.
Settlement follows the auction by a short interval, and the cash leaves your account on the settlement date rather than the bid date. Because the price is below face value, the amount debited is less than the face amount you ordered, and the difference is the return you have already locked in. Nothing about that return depends on anything that happens afterward, provided you hold to maturity.
Competitive versus non-competitive bidding
Every auction accepts two kinds of bid, and the distinction is simpler than the terminology makes it sound. A non-competitive bid says: I will take whatever rate this auction produces, and I want this dollar amount. In exchange for giving up any say in the rate, you are guaranteed to receive the full amount you asked for, subject to a large per-auction limit per bidder.
A competitive bid names a rate. You are saying you will buy only if the auction clears at or above the rate you specified. If it clears below your number, you receive nothing. If it clears at or above it, you may receive all of your order or only part of it, depending on how much demand sits at each level. That uncertainty is the price of expressing an opinion.
Almost every individual buying bills for cash management uses a non-competitive bid, and that is the sensible default rather than a compromise. Competitive bidding is the tool of institutions with a view on where the auction will settle and a reason to care about a basis point. Because auctions clear at a single rate, the non-competitive bidder ends up with the same rate the successful competitive bidders received, which removes most of the apparent disadvantage.
Buying on the secondary market instead
You do not have to wait for an auction. Bills already issued trade continuously, and a brokerage can sell you one with, say, 44 days remaining rather than a fresh 91-day bill. The mechanics are the ordinary mechanics of buying any security: you see a price, or a yield, and you pay a spread between what buyers bid and what sellers ask.
The advantage is precision and immediacy. If you need money back on a particular date that no upcoming auction matches, the secondary market can supply a bill maturing close to it. If you have cash today and the next relevant auction is nine days away, buying an existing bill puts the money to work immediately.
The cost is the spread and, at some brokerages, a commission. On very short bills a spread that looks tiny in price terms can be meaningful in yield terms, because there are so few days left to spread it over. The general rule of thumb is that auctions tend to be the cheaper route for standard terms bought as part of a routine, and the secondary market earns its cost when you need a specific date or immediate execution. Compare the yield quoted net of any commission rather than the headline.
Holding to maturity against selling early
This is where the difference between a bill and a bond fund becomes concrete. A bill held to its maturity date pays face value. Not approximately, not depending on conditions: face value, on the date, assuming the issuer pays. Every rate move between purchase and maturity is irrelevant to that outcome.
A bill sold before maturity pays whatever the market offers that day. That price depends on prevailing short-term rates and on how many days remain, and it can be above or below what you paid. Price risk on a bill is therefore not a property of the instrument; it is a property of the decision to sell.
The size of that risk is unusually small, and the reason is arithmetic rather than luck. A bill’s price converges on face value as the maturity date approaches, because the remaining discount shrinks with the remaining days. That pull toward par is strong and mechanical, and on a short bill it dominates almost everything else. Our note on what a bond ladder is makes the same point for longer maturities, where the convergence is real but takes far longer to rescue you.
How far rates would have to move to hurt you
Put a number on it. Take the illustrative bill again: $10,000 face, bought for $9,797.78, 182 days. Suppose at day 91, exactly halfway, you need the money and sell.
If short rates have not moved, the bill with 91 days remaining prices at $10,000 less 4.00 percent for 91 days on a 360-day basis, which is $9,898.89. You collect $101.11, exactly half the full-term return, which is what you would hope for from half the term.
Now move rates against you. At a 5.00 percent discount rate the same bill prices at $9,873.61, so you collect $75.83 instead of $101.11. You earned less than planned, but you still earned. Push further and the pattern is striking: the break-even point, where the sale returns exactly the $9,797.78 you paid, arrives when the discount rate on the remaining 91 days reaches 8.00 percent. Rates would have to double from 4.00 percent to 8.00 percent, at the halfway mark, before selling early cost you a cent of principal. At 10.00 percent you would receive $9,747.22, a loss of $50.56 on nearly ten thousand dollars. The general rule behind those figures: selling with half the term left breaks even when the rate has doubled, and the further into the bill’s life you sell, the more extreme the move required.
Rolling bills instead of building a ladder
If bills suit you but a single maturity date does not, the standard answer is to roll: buy a bill, and when it matures, buy another of the same term. Do that with 13-week bills and you make four decisions a year; do it with 26-week bills and you make two.
Rolling is not the same thing as a ladder, and the difference matters. A ladder holds several maturities simultaneously, so that money comes back at intervals while the rest stays committed at longer terms. A roll holds one maturity at a time, so the entire sum reprices on each maturity date. A roll is therefore more exposed to the rate on one particular day, and simpler to run.
Which is right depends on whether you need money back at intervals. If the whole sum is a single reserve you do not expect to touch, rolling one bill is less administration for effectively the same result. If you have several dated needs, a small ladder of bills at different terms matches them directly. The design questions are the ones our bond ladder explainer works through, and they apply unchanged when the rungs are bills rather than notes. Note the honest limitation of both: neither locks a rate beyond the term you bought, so a sustained fall in short rates shows up in your income within months.
Bills against a high-yield savings account
Set them side by side on the four dimensions that actually differ, because the rate is the one people compare and the least of the four.
Rate certainty runs to the bill. When you buy, the return is fixed for the term and cannot be revised. A savings rate is variable by design and can be cut the week after you open the account, which our explainer on how high-yield savings accounts work sets out at length. If short rates fall, the bill holder keeps the old rate until maturity and the saver does not.
Liquidity runs to the savings account, decisively. Money in a savings account is generally reachable the same day or the next. Money in a bill either waits for maturity or gets sold at a market price with a spread attached. Effort runs to the savings account too: one deposit and nothing else, against auctions, settlement dates and a reinvestment decision every term.
Tax runs to the bill, by the largest margin of the four, for anyone facing a state or local income tax. On the illustrative figures, that was the difference between a 4.05 percent account and a 4.45 percent taxable-equivalent bill, or roughly $18 on $9,797.78 over half a year. The honest summary: the bill wins on rate certainty and after-tax return, the account wins on access and simplicity, and neither wins outright.
Bills against a money market fund
A money market fund is a pooled vehicle holding a basket of very short-term instruments and paying out the income it collects, with a share price that is typically managed to stay stable. Bills are frequently among the things such funds hold, which is why the comparison comes up so often.
The structural differences are three. A fund’s yield floats continuously as its holdings turn over, so it tracks short rates up and down within weeks, while a bill’s return is fixed at purchase for its term. A fund charges an expense ratio, which comes straight out of the yield you see, and our note on what an expense ratio is covers how much a small percentage compounds into. A fund offers same-day or next-day access without selling into a spread, which a bill does not.
Tax is the murky one and deserves care. Where a fund’s income comes from Treasury securities, that portion may retain the state and local exemption in the hands of the shareholder, but this depends on the fund’s actual holdings during the year, on the state’s own rules, and sometimes on threshold tests the fund must meet. It is not automatic, it is not uniform, and it cannot be assumed from a fund’s name. Verify with the fund’s own tax reporting and with a qualified tax professional rather than generalizing from the treatment of a bill held directly.
What bills are not good for
Bills are cash-management instruments, and treating them as anything else goes wrong quickly. They are not growth assets. A short government security is priced to compensate for lending money briefly to the safest borrower available, which is a modest return by construction, and over long horizons that return has historically been the thing inflation eats first.
Money with a decade-long horizon does not belong in bills. That is the argument our analysis of the 4 percent rule makes from the withdrawal side and our note on portfolio management makes from the allocation side: cash-like instruments are for stability and dated needs, and using them for long-horizon money means paying a large opportunity cost for safety you did not need.
They are also not an emergency fund on their own. An emergency fund’s defining property is that it is available on the day the emergency arrives, and a bill is available on its maturity date or at a market price with a spread. A bill can hold the second layer of a reserve, the part you are confident you will not touch this quarter, while the first layer stays somewhere instantly reachable. And they are not a place to be clever: there is no yield to be reached for here, no credit risk to be taken, and nothing to optimize beyond picking a sensible term and converting the rate properly.
Common mistakes with Treasury bills
The first and largest is the one this explainer is built around: comparing a quoted discount rate against a savings APY. Those are different measurements and the discount rate is always the smaller one. Convert to an investment rate or an effective annual yield first, every time, without exception.
The second is forgetting the state and local exemption when it applies, which on the illustrative figures was the biggest single component of the gap. The third is the reverse error, assuming the exemption is worth something when you live somewhere with no state income tax, where it is worth exactly nothing and the comparison should be made on the effective annual yield alone.
The fourth is buying a term longer than your actual horizon and then having to sell. The fifth is letting maturing proceeds sit uninvested for weeks because no decision was made, which quietly costs more than the rate difference anyone was arguing about. The sixth is treating a bill as an emergency fund. The seventh is over-engineering the whole thing: a rolling 13-week or 26-week bill covers most cash-management needs, and the marginal gain from a more elaborate structure is usually smaller than the effort it costs to maintain. Run your own version of these trade-offs in the companion above or in our calculator before committing to a structure.
The bottom line
A Treasury bill is the simplest instrument in fixed income and the one most often compared incorrectly. It pays nothing along the way, sells below face value, and repays face value at maturity, so the entire return is the gap between the two prices and there is no coupon to reinvest.
The arithmetic that decides most real comparisons is the conversion. On an illustrative 182-day bill with $10,000 of face value quoted at a 4.00 percent discount rate, you pay $9,797.78 and receive $202.22. That same transaction is a 4.14 percent investment rate and a 4.18 percent effective annual yield, and for a reader facing an illustrative 6 percent combined state and local marginal rate it is worth the same as a fully taxable 4.45 percent. The quoted headline understated the comparable figure by 0.45 points, and the tax exemption alone was 0.27 of them.
The rest follows from purpose. Pick a term you can genuinely wait out, use a non-competitive bid, hold to maturity so price risk never becomes real, and remember that selling at the halfway point on the illustrative bill would take a doubling of rates before it cost you principal. Bills are for money that is not investment capital and is not needed tomorrow. For everything shorter, keep a savings account; for everything longer, own something that grows.
Dividora writes for readers who would rather see the arithmetic than be handed a conclusion, and that is all this explainer is: general educational information, not financial, tax or investment advice, and not a recommendation to buy any security, open any account, or use any particular platform or provider. Every rate, price, day count, dollar return and tax rate above was invented to make the mechanism legible, and none of them quotes a real auction, a real market or a real product. Real bill prices, auction results, term schedules, purchase minimums and bidding limits change and should be read from the Treasury’s own published material on the day you act. The claim that Treasury interest is exempt from state and local income tax is stated as the general rule and nothing more: exemptions, thresholds, reporting requirements and the timing of when a bill’s return becomes taxable all depend on your jurisdiction and your own circumstances, and they change. Confirm your position with a qualified tax professional, and take the question of whether short government securities suit your situation at all to a qualified financial adviser who can see your full picture.
Frequently asked questions
What are Treasury bills in simple terms?
A Treasury bill is a short-term loan you make to the government, structured so that you pay less than the face value up front and receive the full face value when the bill matures. There is no interest payment along the way. The whole return is the difference between what you paid and what you get back. On an illustrative 26-week bill with a face value of $10,000 quoted at a 4.00 percent discount rate, you would pay about $9,797.78 and receive $10,000 at maturity, a return of $202.22 over 182 days. Every figure here is illustrative arithmetic chosen to make the mechanism legible, not a quote of any current market rate.
What is the difference between the discount rate and the investment rate on a T-bill?
They are two different ways of annualizing the same dollar return, and they produce different numbers. The discount rate divides the return by the face value and annualizes on a 360-day year. The investment rate, also called the coupon equivalent or bond equivalent yield, divides the same return by the price you actually paid and annualizes on a 365-day year. Both are correct within their own conventions, but only the investment rate answers the question a saver is asking. On the illustrative bill above, the discount rate is 4.00 percent while the investment rate is 4.14 percent, and the second is the one to carry into any comparison.
Are Treasury bills exempt from state income tax?
As a general rule, interest on Treasury securities, including bills, is subject to federal income tax but exempt from state and local income taxes. That exemption is the part of a bill's return that a headline rate never shows. For an illustrative reader facing a 6 percent combined state and local marginal rate, a bill yielding an effective 4.18 percent a year is worth roughly the same after tax as a fully taxable account paying 4.45 percent. Tax rules change, vary by state, and depend on your own circumstances, so confirm the current treatment with the relevant tax authority's own material or with a qualified tax professional before relying on it.
How much do I need to buy a Treasury bill?
Bills are commonly available in small denominations, typically a $100 minimum with purchases in $100 increments through the government's own purchase channel, which puts them within reach of almost any saver. Brokerages that offer bills may set their own higher minimums and their own increments, so the practical floor depends on where you buy. Because the purchase price is below face value, the cash you commit is slightly less than the face amount you order. Confirm current minimums and increments with the Treasury's own material or with your broker, since these are administrative details that can be revised.
What happens if I need my money before the bill matures?
You can sell a bill on the secondary market through a broker before it matures, and the price you receive is whatever a buyer will pay that day, which depends on prevailing short-term rates and how many days remain. That is the only situation in which a bill carries price risk. Because a bill's price climbs toward face value as the maturity date approaches, short bills are unusually forgiving: on the illustrative 182-day bill above, sold at the halfway point, rates would have to double from 4.00 percent to 8.00 percent before the sale returned less than the $9,797.78 you paid. That is illustrative arithmetic, not a promise about any real bill.
Are T-bills better than a high-yield savings account?
Neither is better in general, because they solve slightly different problems. A bill locks a known return for a known term and carries a state and local tax exemption; a savings account keeps the money reachable the same day but pays a rate that can be cut without notice and is usually taxable at every level. On the illustrative figures used throughout this explainer, a bill quoted at 4.00 percent and a savings account paying 4.05 percent APY are not close: after a 6 percent state rate, the bill leaves roughly $18 more on about $9,798 committed for 182 days. Whether that gap justifies the extra effort and the loss of instant access is a personal question, not a general answer.
What is the difference between competitive and non-competitive bidding?
A non-competitive bid says you will accept whatever rate the auction produces, and in exchange you are guaranteed to receive the full amount you asked for, up to a large per-auction cap. A competitive bid names the discount rate you are willing to accept, and you may receive all of your order, part of it, or none, depending on where the auction clears. Almost everyone buying bills as a saver uses non-competitive bidding, because the alternative requires a view on where the auction will settle and risks going home empty-handed. Confirm current bidding limits and procedures with the Treasury's own material.
Do Treasury bills pay interest?
Not in the way a coupon bond does. A bill makes no periodic payments at all, which is why it is described as a zero-coupon instrument. Its entire return arrives as a single event at maturity, when the face value is paid and the difference over your purchase price becomes your earnings. That structure removes the reinvestment problem that coupon bonds create, since there is no stream of small payments to redeploy, and it replaces it with a single larger reinvestment decision on the maturity date. All figures used to illustrate this are chosen for clarity rather than drawn from any current market.
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