Wash Sale Rule: 30-Day Timing, Replacement Shares, ETFs, and IRA Traps

📅 Rule basis reviewed: August 18, 2026

How the Wash Sale Rule Uses the 61-Day Period

Start with the loss-sale date. Treasury Regulation §1.1091-1 describes the relevant span as the 61-day period, beginning 30 days before the sale and ending 30 days after it. That matters because purchases made before the loss sale can count too. Waiting 30 days after you sell does not erase a replacement purchase that already occurred inside the pre-sale side of the period.

For example, suppose you sell shares at a loss on April 30. The 61-day period runs from March 31 through May 30. If you bought substantially identical shares on April 12, that acquisition occurred before the loss sale, but it is still inside the period. A reader who checks only what happens after April 30 would miss it.

A date match is only a screening result. The federal rules cover purchases of substantially identical stock or securities, acquisitions in a fully taxable trade, and contracts or options to acquire substantially identical stock or securities. The rules can also apply when substantially identical stock is acquired for your IRA or Roth IRA. Publication 550 further warns that certain purchases by a spouse or by a corporation you control can produce a wash sale.

That is why the wash sale rule works better as a sequence than a slogan: find the relevant acquisitions, test substantial identity, identify the account, and then match the shares.

Quick sequence: 61-day period → same or substantially identical security? → which account? → how many shares? → reporting.

Source: Treasury Regulation §1.1091-1 and IRS Publication 550, “Wash Sales.” Read the regulation · Read Publication 550.

ETFs Are Where “Substantially Identical” Gets Murky

The dates are the easy part. ETFs are where the analysis gets less comfortable.

Buying the exact same ETF inside the 61-day period is the straightforward case. Switching to a different ETF is harder because Publication 550 does not give investors an ETF-by-ETF safe list. Instead, it says whether stock or securities are substantially identical depends on the facts and circumstances.

That means a new ticker symbol, fund name, or issuer does not create a tax-law safe harbor by itself. It also means economic similarity alone does not automatically prove that two funds are substantially identical. The wash sale rule asks a legal tax question, not merely whether two charts tend to move together.

This matters in tax-loss harvesting because two broad-market ETFs can look interchangeable while differing in index construction, holdings, weighting, or strategy. Those facts may matter, but the IRS has not published a simple ETF-pair whitelist.

So avoid turning common portfolio practice into an IRS rule. A more conservative replacement approach is to preserve the investment role while moving to a meaningfully different index or strategy. That may reduce uncertainty, but it is still a risk-management choice, not an IRS guarantee.

A useful practical question is: what actually changed besides the ticker? A genuinely different benchmark or strategy gives you more to distinguish, but it still does not create a universal safe harbor.

Think of ETF replacements as a spectrum, not a whitelist. When a close ETF pair creates a material tax consequence and the answer is genuinely uncertain, qualified tax advice is more useful than forcing a confident yes-or-no answer from incomplete guidance.

Source: IRS Publication 550, “Substantially identical.” Open the IRS guidance.

Where You Rebuy Changes What Happens to the Loss

Here is the part many investors miss: once the wash sale rule applies, the account holding the replacement can change what happens to the disallowed loss.

For an ordinary taxable-account replacement, Publication 550 says the disallowed loss is generally added to the basis of the replacement stock or securities. The old holding period also carries over. In other words, the rule commonly postpones recognition of that loss by moving it into the basis of the replacement position.

If a taxable replacement purchase causes $400 of loss to be disallowed, that $400 is generally added to the basis of the matched replacement shares. The loss has moved into basis rather than simply disappearing from the record.

An IRA or Roth IRA can be much less intuitive. Revenue Ruling 2008-5 addresses a taxpayer who sells stock at a loss in a taxable account and causes an IRA or Roth IRA to buy substantially identical stock inside the relevant period. The ruling says the loss is disallowed, but the IRA or Roth IRA basis is not increased under section 1091(d).

That is the IRA trap worth remembering. You should not automatically carry the taxable-account shortcut, “add the disallowed loss to replacement basis,” into the retirement-account fact pattern addressed by Revenue Ruling 2008-5.

Keep the ruling’s scope narrow. It resolves the facts it addresses and explicitly says it does not address issues beyond them. The account label also does not replace the substantial-identity analysis. A purchase in an IRA matters only if the other elements of the wash sale rule line up.

Sources: IRS Publication 550 for taxable replacement basis and holding-period treatment; Revenue Ruling 2008-5 for the taxable-sale/IRA-or-Roth-IRA fact pattern. Publication 550 · Rev. Rul. 2008-5.

A Wash Sale Can Hit Only Part of the Trade

A wash sale does not automatically contaminate every share in a larger loss sale. The matching rules work at the share level.

Suppose you bought 100 shares at $50 and later sold all 100 at $40, creating a $1,000 loss. Twelve days later, you bought 40 substantially identical shares in a taxable account at $42.

• You sold 100 loss shares.
• You bought 40 qualifying replacement shares.
• In this simple one-lot example, 40 loss shares are matched.
• The disallowed loss is $400: 40 shares × $10 loss per share.
• The 40 replacement shares cost $1,680. Adding the $400 disallowed loss produces an adjusted basis of $2,080, or $52 per share.

In this simple case, replacing 40% of the shares really does make 40% of the dollar loss subject to the wash sale rule. That shortcut stops being reliable when sold lots have different losses per share or several replacement acquisitions must be matched.

The regulations also specify acquisition-order matching. When replacement quantity differs from the number of loss shares sold, acquired shares are matched in the order they were acquired, beginning with the earliest acquisition. So if you make several qualifying purchases inside the 61-day period, you cannot safely treat them as one undifferentiated block and pick whichever matching order gives the preferred result.

For another pattern, suppose you sell 100 shares at a loss after buying 20 substantially identical shares eight days earlier, then buy 20 more twelve days after the sale. Both purchases sit inside the same 61-day period, so both can enter the matching analysis if the other requirements are met.

That is why share count should come before dollar shortcuts. Identify the relevant acquisitions, order them correctly, match the shares, and then calculate the loss attached to the matched sold lots.

Source: Treasury Regulation §1.1091-1(c)–(d) and IRS Publication 550, “More or less stock bought than sold.” Read the matching rule · Publication 550.

Your Broker May Not Catch the Whole Thing

The broker flag is useful. It is not a complete tax answer, because the wash sale rule is broader than the broker-reporting rule.

Publication 550 says Form 1099-B shows a disallowed wash-sale loss in box 1g when the sold stock or securities are covered securities and the substantially identical replacement stock or securities have the same CUSIP and were bought in the same account. The IRS also says you cannot deduct a wash-sale loss merely because Form 1099-B did not report it.

A cross-account purchase can therefore matter even when a single broker statement does not connect the transactions for you. Certain spouse or controlled-corporation purchases can matter too.

Automatic purchases deserve the same attention. A dividend reinvestment can quietly buy additional shares while you are focused on selling another lot for a tax loss. The fact that the acquisition happened automatically does not make the timing question disappear. The security still has to be the same or substantially identical, but the purchase should be included in the review rather than ignored because you did not manually place the order.

Once you know a wash sale actually occurred, the reporting step comes last. The 2025 Instructions for Form 8949 use code W in column (f) and require the nondeductible wash-sale loss to be entered as a positive amount in column (g). If the broker-reported wash-sale amount is wrong, the instructions tell you to enter the correct nondeductible amount and, in some circumstances, attach an explanation.

The sequence matters. Form 1099-B and Form 8949 are reporting tools; they are not substitutes for the underlying wash sale rule. First determine the transaction result from the dates, security, account, and matching facts. Then use the tax forms to report that result correctly.

Sources: IRS Publication 550, “Nondeductible wash sale loss,” the 2025 Instructions for Schedule D, “Wash Sales,” and the 2025 Instructions for Form 8949, “How To Complete Form 8949, Columns (f) and (g).” Publication 550 · Schedule D instructions · Form 8949 instructions.

Five Checks Before You Harvest the Loss

Before you treat a tax loss as usable, run these five checks in order. The point is not to turn every trade into a tax project. It is to catch the small number of facts that can change the result.

1. Dates: look 30 calendar days before and 30 calendar days after the loss sale. Include purchases that occurred before the sale, not just what you plan to buy afterward.
2. Security: ask whether any acquisition is the same or substantially identical. Do not treat a different ETF ticker as an automatic safe harbor.
3. Account: identify where the replacement was acquired. Taxable accounts, IRAs, Roth IRAs, and certain spouse or controlled-corporation activity can lead to different reporting or basis consequences.
4. Quantity: match replacement shares to loss shares at the share and lot level. When several purchases are involved, preserve acquisition order rather than relying on a percentage shortcut.
5. Reporting: compare your tax-rule result with Form 1099-B and Form 8949. A missing broker flag is not proof that the loss is deductible.

One habit makes the wash sale rule easier to manage: keep a compact trade record with the loss-sale date, acquisition date, shares, account, security, reinvestment status, and broker flag. If substantial identity is uncertain, record why instead of silently assuming the replacement is safe. This becomes especially useful near year-end when several accounts, lots, and reinvestments overlap.

The final logic is simple: timing finds the candidates. Substantial identity determines whether the security can match. The account changes the consequence. Share matching determines how much of the loss is affected. Broker reporting comes last. If those five questions are answered, the wash sale rule becomes far more manageable than the usual “30-day rule” shorthand suggests.

If a close ETF pair or unusual account setup leaves the substantial-identity question unresolved, do not use a missing broker flag as permission to claim the loss. Resolve the uncertainty before relying on the deduction.

Sources

• IRS Publication 550 (2025), “Wash Sales”
• Treasury Regulation §1.1091-1
• Revenue Ruling 2008-5
• 2025 Instructions for Schedule D (Form 1040)
• 2025 Instructions for Form 8949

Educational quantitative analysis based on published data. Not investment, tax, or legal advice. Consult a licensed professional before acting on any calculation. About TheFinSense.