What Is a Wash Sale? The 30-Day Rule, Explained

Selling a losing position to claim the tax deduction, then buying it straight back so you keep the exposure, is such an obvious manoeuvre that the tax code closed it a very long time ago. The wash sale rule is the closure. It says that if you sell at a loss and re-establish essentially the same position within a defined window, you do not get to use the loss this year.

That much most investors know. What catches people is everything around it: the window runs backwards as well as forwards, an automatic dividend reinvestment can trigger it without any decision on your part, a purchase in a retirement account can destroy the loss rather than defer it, and your broker’s reporting does not see across institutions. This ledger note is about the rule itself rather than the strategy it constrains. If what you want is the process of harvesting losses deliberately, our note on how to do tax-loss harvesting walks that step by step. This page covers what a wash sale is, the 61-day window, what substantially identical means, where the disallowed loss goes, and how brokers report it. Run your own position through the retirement calculator if you want the portfolio context, and the companion above works the disallowed portion from your own numbers.

The short answer: a wash sale is a loss sale paired with a purchase of the same or a substantially identical security within 30 days before or 30 days after. The loss is disallowed for the year and generally added to the basis of the replacement shares, so it is deferred rather than destroyed. The exception is a repurchase inside an IRA, where it is commonly described as lost outright.

What a wash sale actually is

A wash sale occurs when an investor sells a security at a loss and, within a defined window around that sale, acquires the same security or one that is substantially identical to it. The consequence is that the loss is disallowed for the tax year in which the sale occurred, so it cannot be used on that year’s return to offset capital gains or ordinary income.

The word wash is doing useful work in the name. From an economic standpoint, selling a position and immediately buying it back leaves you where you started: the same exposure, the same risk, the same future returns. The only thing that changed is that a paper loss became a realised one on the tax return. The rule takes the view that a transaction which washes out economically should not generate a tax benefit, and disallows it.

Two boundaries are worth setting immediately because they prevent a lot of confusion. First, the rule applies only to sales at a loss. Selling at a gain and repurchasing immediately does not create a wash sale, and the gain is fully taxable. Second, the rule does not eliminate the loss in the ordinary case; it moves it. Understanding where it moves is most of the practical content of this note.

The rule sits in the tax code and has been in place for many decades, so it is a settled feature of United States taxation rather than a recent development. Its exact application to particular securities and situations is where the difficulty lives, which is why every section below ends up pointing at the same conclusion: confirm your facts with a tax professional.

The 61-day window and why people miss half of it

The window is described as 30 days before the sale and 30 days after the sale. Adding the day of the sale itself, that is a total of 61 days during which a purchase of the same or a substantially identical security can trigger the rule.

Most investors picture only the forward half. They sell at a loss, note that they must not buy back for a month, mark a date on the calendar, and consider the problem handled. The backward half catches them because it requires remembering something rather than planning something: a purchase made three weeks before the loss sale, possibly for entirely unrelated reasons, is inside the window and can trigger the rule just as effectively.

The common practical guard is to treat 31 days after the sale as the earliest date to repurchase, since counting rules around the boundary are easy to get wrong by one day and the cost of a mistake is the whole loss. On the backward side, the guard is a review rather than a wait: before selling at a loss, check every account for any purchase of that security in the preceding month, including automatic ones.

Because the precise day counting can matter and because your situation may involve facts this note does not anticipate, treat these as general descriptions and confirm the treatment of your own trades with a qualified tax professional.

What substantially identical means

This is the least precise phrase in the rule and the source of most of its genuine uncertainty. Substantially identical describes a replacement security that is close enough to the one you sold that acquiring it re-establishes essentially the same position.

Some cases are clear. Shares of the same company are substantially identical to other shares of the same company. The same fund is substantially identical to itself, including the same fund bought at a different broker or in a different account. Options to acquire the same stock are generally treated as within scope, as are contracts to acquire it.

Some cases are clearly outside. Two different companies in the same industry are not substantially identical to each other simply because their businesses are similar, and a broad market fund is not substantially identical to a single stock inside it.

The genuinely contested territory is between those poles, and the clearest example is two different fund providers’ index funds tracking the same underlying index. They hold essentially the same securities in essentially the same weights, which sounds substantially identical, yet they are separate legal entities with different sponsors, different expense structures, and different share classes. There is no published bright line resolving this, and reasonable practitioners take different views.

The honest advice is therefore not an interpretation but a posture. Where the boundary is unclear, cautious investors avoid relying on it, either by waiting the full period or by choosing a replacement that is clearly different in its exposure rather than nearly identical. If you intend to rely on a distinction, that is a conversation to have with a tax professional in advance rather than a judgement to make alone.

Where the disallowed loss goes

The most reassuring thing about the rule in the ordinary case is that a disallowed loss is generally not destroyed. It is added to the cost basis of the replacement shares.

Work it through on illustrative numbers. You bought 100 shares at $50, a $5,000 position. You sell them at $30, receiving $3,000 and realising a $2,000 loss. Within the window you buy 100 shares back at $32, spending $3,200. The $2,000 loss is disallowed for this year, and it is added to the basis of the new shares, so their basis becomes $3,200 plus $2,000, which is $5,200 rather than $3,200.

The consequence appears later. Suppose the shares recover and you eventually sell them at $60, receiving $6,000. With the adjusted basis of $5,200 your gain is $800. Without the adjustment it would have been $2,800. The $2,000 you could not deduct this year has reduced your taxable gain by exactly that amount when you finally exit.

That is the sense in which the rule defers rather than denies. The timing changes, which can matter for cash flow and for which tax year the benefit lands in, but the economic amount is preserved as long as you eventually sell the replacement shares in a taxable account. The two situations where that preservation breaks down, an IRA repurchase and never selling, get their own treatment below.

The holding period carries across too

A second adjustment accompanies the basis change and is less well known. The holding period of the shares you sold is generally added to the holding period of the replacement shares.

That matters because of the distinction between short term and long term capital gains treatment, which generally turns on whether a position was held for more than one year. A position you had held for eleven months and sold at a loss, then repurchased inside the window, does not restart its clock at zero on the replacement shares; the earlier holding period generally carries over, so the replacement shares can reach long term status sooner than a fresh purchase would.

This is one of the few genuinely favourable aspects of a wash sale, and it is easy to overlook because it only matters when you eventually sell. It is also a reason not to panic about an accidental wash sale on a position you intend to hold anyway: the loss defers into basis, the clock continues, and the practical damage is a timing difference rather than a loss of value.

The corollary is a record keeping obligation. If both the basis and the holding period of your replacement shares differ from what a naive reading of the purchase confirmation would suggest, then your own records need to reflect that, particularly if the shares later move between institutions. Our note on how to open a brokerage account touches on the transfer process where basis information can go astray.

Partial repurchases and proportional disallowance

The rule does not operate as an all or nothing switch. If you repurchase fewer shares than you sold, the disallowance is generally proportional to the number of replacement shares acquired.

Continue the illustrative example. You sold 100 shares at a $2,000 loss. If you repurchase only 25 shares within the window, roughly a quarter of the loss is disallowed, so about $500 is deferred into the basis of those 25 shares and about $1,500 remains deductible this year. Repurchase 50 shares and about $1,000 is disallowed. Repurchase all 100 and the entire $2,000 is disallowed.

That proportionality is genuinely useful to know, because it changes how alarming an accidental trigger is. An investor who harvested a large loss and then discovered that a single reinvested dividend bought three shares inside the window has not lost the whole deduction; they have deferred a small proportion of it. The problem is real but rarely catastrophic, and knowing that prevents an overreaction such as selling the replacement shares in a panic.

Note also that repurchasing more shares than you sold does not disallow more than the loss itself. The disallowance is capped by the size of the loss.

The IRA trap

This is the version of the rule that genuinely destroys value rather than deferring it, and it deserves emphasis because it is easy to trigger unintentionally.

If you sell a security at a loss in a taxable account and acquire the same or a substantially identical security inside an IRA within the window, the loss is generally disallowed, and the usual rescue does not operate. The basis adjustment that normally preserves the loss depends on the replacement shares carrying a taxable cost basis, and shares inside a traditional or Roth IRA do not work that way for this purpose. The commonly cited result is that the loss is permanently lost rather than deferred.

The reason this is easy to trigger is that retirement accounts are frequently on autopilot. Contributions arrive on a schedule, target date funds and model portfolios buy automatically, and dividends reinvest without anyone deciding. An investor who deliberately harvests a loss in a brokerage account may have no idea that a purchase of an overlapping fund occurred in their IRA in the same window.

The guard is a pre-harvest check rather than a rule of thumb. Before selling at a loss, look at every account you control, including retirement accounts, and confirm that nothing has bought or will buy the same or a substantially identical security within the window. Where an automatic contribution is scheduled, either pause it or choose a different date for the harvest. Because the mechanics here are consequential and depend on your specific accounts, confirm the treatment with a tax professional before acting.

Spouses controlled entities and other accounts

The rule is not confined to a single account or, in some circumstances, to a single person. Purchases by a spouse are commonly treated as being within scope, and so are purchases by an entity you control. The reasoning is the same as the rule itself: if the household or the controlled entity has re-established the position, the economic wash has occurred regardless of whose account holds the shares.

That widens the pre-harvest check considerably. A household where two people manage separate brokerage accounts, each with their own automatic investing, has more surface area for an accidental trigger than a single investor with one account. So does an investor who also directs purchases inside a trust, a business account, or a custodial account for a child.

The practical response is to treat the check as household wide rather than account wide, and to have the conversation before the harvest rather than at tax time. It only takes one message to confirm that nobody is buying the same fund next week.

None of this is intended to describe every relationship or entity structure the rule can reach, because those situations vary a great deal and depend on facts. If your household holds meaningful positions across multiple people or entities, that is a good reason to have a tax professional look at the harvesting plan before you execute it rather than after.

Dividend reinvestment as an accidental trigger

The single most common accidental wash sale has nothing to do with a trading decision. It is an automatic dividend reinvestment landing inside the window.

The mechanism is simple. You hold a position that pays a dividend, and you have reinvestment switched on, so every distribution automatically buys additional shares of the same security. If a distribution falls within the 61-day window around a loss sale, that automatic purchase is an acquisition of the same security, and a portion of the loss is disallowed accordingly.

Because the amounts involved are usually small relative to the position, the disallowance is usually small too, thanks to the proportionality described above. But it is entirely avoidable, and the fix is one setting.

The habit worth adopting is to switch off automatic reinvestment on any position you are considering harvesting, well before the harvest, and to remember that distributions can also arrive in the 30 days before a sale. Our notes on dividend reinvestment plans and on how to set up a DRIP cover how the mechanism works, and our note on reinvesting dividends touches on the same trap from the other direction. Reinvestment is a good default for long term compounding and a bad default during a harvest window, and the skill is simply remembering to toggle it.

Automatic investing and scheduled contributions

Dividend reinvestment is not the only autopilot. Scheduled contributions to a brokerage account, payroll deductions into a workplace plan, robo-advisor rebalancing, and model portfolio adjustments all buy securities on dates nobody actively chooses.

Each of those is a potential trigger if it acquires the same or a substantially identical security inside the window. Workplace retirement plan contributions deserve particular attention because they combine two of the riskier features: they are automatic, and they land in a retirement account, which is where a wash sale is commonly described as destroying the loss rather than deferring it.

Robo-advisors and managed portfolios add a further wrinkle, because the buying decisions are made by an algorithm or a manager rather than by you, and you may not know in advance what will be purchased. Many such services perform their own harvesting and their own wash sale avoidance internally, but they cannot see the accounts you hold elsewhere.

The practical response is a scheduling one. Before a harvest, list every automatic purchase in every account and note its next date. If any of them will buy an overlapping security within the window, either pause it, redirect it to something clearly different, or move the harvest date. This is a ten minute exercise that prevents the most common failure mode entirely, and it is worth building into the harvesting routine our note on tax-loss harvesting sets out.

Options and derivatives

The rule reaches beyond straightforward share purchases. Acquiring an option or a contract to acquire the same stock is generally treated as an acquisition for these purposes, which means that selling a stock at a loss and buying a call option on it within the window can trigger the rule.

The reasoning is consistent with everything else here: an option to buy the stock re-establishes economic exposure to it, so the position was not genuinely exited. The same logic extends to certain other contractual arrangements that restore the position.

The interaction between the wash sale rule and options strategies gets complicated quickly, because options carry their own basis, expiry, and assignment mechanics, and because writing a deep in the money put can look economically similar to owning the stock. This is an area where general descriptions are particularly unreliable and where the facts of a specific trade matter a great deal.

If your investing involves options alongside the underlying shares, treat the interaction as a question for a tax professional rather than something to reason out from a general article. The purpose of mentioning it here is simply so you know the exposure exists, because an investor who thinks the rule only applies to buying shares back can walk into it without realising there is anything to check.

How brokers report wash sales

Brokers generally identify and report wash sales on the tax documents they issue, and modern reporting is considerably better than it once was. Two limitations matter enormously.

The first is scope. A broker sees the accounts you hold with that broker. It does not see the account you hold at another institution, and it does not see your spouse’s account elsewhere. A loss sale at one firm and a repurchase at another will typically not be flagged by either of them, and the obligation to report it correctly is still yours.

The second is interpretation. Broker systems generally track identical securities, commonly matched by the security identifier, rather than making a judgement about what is substantially identical. That means two different providers’ funds tracking the same index will usually not be flagged even in circumstances where a conservative reading might treat them as within scope.

The conclusion is not that broker reporting is unreliable, because it is a genuinely useful input. The conclusion is that it is a floor rather than a ceiling: what a broker flags is almost certainly a wash sale, but what it does not flag is not thereby cleared. Your return is prepared on your facts across all your accounts.

Practically, that argues for keeping your own record of loss sales and the dates around them, particularly if you hold accounts at more than one institution. A short note of what was sold, when, and what was bought in the surrounding month is enough to answer the question later, and it is far easier to write at the time than to reconstruct in April.

The rule applies to losses only

It is worth stating plainly because it removes an entire category of unnecessary worry: the wash sale rule applies only to sales at a loss.

If you sell a position at a gain and buy it straight back the same afternoon, no wash sale arises. The gain is realised and taxable in that year, and the new shares start with the price you paid as their basis. This is sometimes described as gain harvesting, and while it has its own considerations, the wash sale rule is not among them.

The asymmetry follows from the rule’s purpose. It exists to prevent an artificial tax benefit, and realising a gain produces a tax cost rather than a benefit, so there is nothing to prevent.

The practical implication is that rebalancing which realises gains is not constrained by the rule, while rebalancing which realises losses is. Our note on rebalancing a portfolio covers the mechanics, and the wash sale check only needs to be applied to the loss side of the exercise. That is a useful simplification, because it means you do not need to think about the 61-day window every time you trade, only when a trade realises a loss.

Digital assets and where the rule currently sits

The rule as written addresses stocks and securities, and whether it applies to digital assets such as cryptocurrencies has been an active question. Proposals to extend wash sale treatment to digital assets have circulated in legislative discussion, and commentary on the topic ages quickly.

Because this is precisely the kind of point where a confident statement becomes wrong without warning, this note deliberately does not assert the current position. What is worth knowing is that the question exists, that the treatment has been the subject of proposed change, and that anyone whose tax planning depends on the answer should confirm the current law with a tax professional rather than relying on any article, including this one.

The wider caution generalises. Tax rules change, thresholds are revised, and the interpretation of terms like substantially identical develops through guidance and practice. Everything described in this note reflects how the rule is commonly explained rather than a statement of current law applicable to your circumstances.

If you are in a position where the answer materially affects a decision, the cost of an hour with a qualified professional is small relative to the amount usually at stake, and it also gets you an answer specific to your accounts rather than a general one.

How to avoid a wash sale

Three approaches cover almost every case, and they can be combined.

The first is to wait. Sell at a loss, then do not acquire the same or a substantially identical security for more than 30 days, which is commonly implemented as waiting 31 days to leave no ambiguity at the boundary. Pair that with a backward check confirming nothing was bought in the preceding month.

The second is to substitute. Rather than sitting in cash for a month and risking a rally you miss, buy a different security that gives broadly similar exposure without being substantially identical. The risk here is that the boundary is not precisely defined, so how far the substitute must differ is a judgement rather than a calculation, and a conservative substitution differs in a way you could defend rather than one that is nearly the same thing under a different ticker. This is a question worth putting to a tax professional in advance.

The third is to prepare. Before any harvest, switch off dividend reinvestment on the position, pause or redirect automatic purchases, check retirement accounts and household accounts, and note the date so the forward window is tracked. Most accidental wash sales are caused by autopilot rather than by decisions, so the preparation step prevents more of them than the analysis does.

Whichever route you take, the sequencing our note on tax-loss harvesting describes puts these steps in the right order relative to the trade itself.

What to do if you triggered one

Discovering an accidental wash sale is uncomfortable and usually less serious than it feels. Several things are worth knowing.

In the ordinary case, in a taxable account, the loss is deferred rather than destroyed: it moves into the basis of the replacement shares and comes back when you sell them. The damage is a timing difference.

The disallowance is proportional, so a small accidental purchase disallows a small proportion of the loss rather than all of it.

The holding period generally carries over, which can slightly favour you later.

The one genuinely bad case is the retirement account repurchase, where the loss is commonly described as lost, and there is no obvious remedy after the fact.

What you should not do is compound the problem by trading reactively. Selling the replacement shares immediately to fix things can create fresh consequences and is unlikely to restore the original loss. The right response is usually to record what happened, adjust your basis records to reflect the deferral, and get the reporting right on the return, which is a conversation with whoever prepares it.

Then fix the cause rather than the symptom: turn off the automatic purchase that triggered it, and add the pre-harvest check to your routine so the same thing does not recur next year.

Common misconceptions

• That the window is only forward. It runs 30 days before as well as after, and the backward half is the one that catches people.
• That the loss disappears. In a taxable account it is generally added to the replacement shares’ basis, so it returns when they are sold. The IRA case is the exception.
• That it applies to gains. It applies only to sales at a loss.
• That the broker will catch it. Brokers see their own accounts and generally match identical securities. Cross-institution and household activity is yours to track.
• That any similar fund is safe. Two providers’ funds tracking the same index sit in genuinely unsettled territory rather than being clearly outside the rule.
• That selling and rebuying in an IRA is harmless. A loss sale in a taxable account paired with a purchase inside an IRA is the worst outcome available under the rule.
• That one reinvested dividend ruins the whole loss. The disallowance is proportional, so a small purchase disallows a small slice.

Each of these comes from treating the rule as simpler than it is in one direction while treating its consequences as more severe than they are in another.

A worked example end to end

Theory into practice on illustrative figures throughout. Our investor holds 100 shares bought at $50, a $5,000 position, now trading at $30. She wants the tax loss and also wants to keep exposure to the sector.

She prepares first. She switches off dividend reinvestment on the position. She checks her brokerage for scheduled purchases and finds a monthly automatic buy of the same fund set for eleven days after her intended sale date, which she pauses. She checks her workplace retirement plan and confirms its next contribution does not buy an overlapping fund. And she looks backwards, confirming she bought nothing in that security in the previous month.

She sells, receiving $3,000 and realising a $2,000 loss.

Case one, the mistake. Suppose she had bought 100 shares back at $32 twenty days later, spending $3,200. The $2,000 loss would be disallowed for the year, the basis of the new shares would become $5,200 rather than $3,200, and the old holding period would carry across. If she later sold at $60, receiving $6,000, her gain would be $800 rather than $2,800. Nothing was lost, but the deduction moved to a later year.

Case two, the partial mistake. Suppose only a reinvested dividend had slipped through and bought 5 shares inside the window. Roughly 5 percent of the loss, about $100, would be disallowed and deferred into those 5 shares, and about $1,900 would remain deductible this year. Irritating, not serious.

Case three, what she actually did. She waited 31 days, holding a clearly different broad market fund in the interim to stay invested, then repurchased the original position. The full $2,000 loss stands for the year, available to offset gains and, up to a commonly cited annual limit that you should confirm for the current year, ordinary income, with any remainder carried forward. Our note on tax-loss harvesting covers how that offsetting works, and our note on dividend income tax covers the wider tax picture around a portfolio. Run your own numbers through the companion above, and confirm the treatment with a tax professional before filing.

The bottom line

A wash sale is a loss sale paired with a purchase of the same or a substantially identical security inside a window that runs 30 days before the sale and 30 days after it, 61 days in total. When it happens the loss is disallowed for that year, and in a taxable account it is generally added to the replacement shares’ cost basis along with the old holding period, so the benefit is deferred rather than destroyed. Three things account for most of the trouble people have with it. The window runs backwards as well as forwards, and almost nobody checks the backward half. Automatic purchases, especially reinvested dividends and scheduled contributions, trigger it without any decision being made, which is why switching off reinvestment and pausing automatic buys is the single most effective preventive step. And a repurchase inside an IRA is the one version that commonly destroys the loss outright rather than deferring it, which makes a household wide account check the step to take before any harvest rather than after. Brokers report what they can see within their own walls, which is useful and incomplete, so keep your own note of loss sales and the month either side. And because substantially identical has no published bright line and tax rules change, take any plan that depends on the boundary to a qualified tax professional before you execute it rather than after you file.

This ledger note describes how the wash sale rule is commonly explained and is general educational information, not tax, legal, or investment advice, and it is not tailored to your circumstances. Every share count, price, basis figure, and loss amount used here is illustrative arithmetic chosen to demonstrate the mechanics rather than to compute any real tax result. Tax law changes, thresholds and annual limits are revised, and the application of terms such as substantially identical develops through guidance and practice, so nothing here should be treated as a statement of current law. The treatment of digital assets under this rule in particular has been the subject of proposed change and is deliberately not asserted here. Confirm the current rules and the treatment of your own trades with a qualified tax professional before harvesting a loss or filing a return that relies on one.

Edited by Hamza Hai, MBA · Editor

Hamza Hai is the editor of Dividora. She holds an MBA and reviews the site's articles against our editorial standards, checking that every figure is labelled for what it is, that nothing is presented as verified fact without a source the reader can check, and that the writing stays useful to a non-specialist.

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