The wash sale rule is simple to state and messy everywhere it touches ETFs. Sell a security at a loss, buy the same or a "substantially identical" security within 30 days before or after, and the IRS disallows the loss for that year. The rule dates to 1921. The phrase "substantially identical" has never been formally defined for funds. That gap is where every interesting question about ETF tax-loss harvesting lives, and where the genuinely expensive mistake, the IRA repurchase, hides.
The Window Is 61 Days, Not 30
The rule, from Section 1091 of the tax code, covers 30 days before the sale, the day of the sale, and 30 days after it: a 61-day window. Buying shares on June 20, selling other shares of the same fund at a loss on July 10, and never touching it again still triggers a wash sale, because the June purchase landed inside the window. The "before" half surprises people far more often than the "after" half.
Three mechanics matter:
- The loss is deferred, not destroyed. The disallowed amount gets added to the cost basis of the replacement shares. Sell 100 shares bought for $10,000 at $8,500, rebuy 12 days later for $8,800, and your new basis is $8,800 plus the disallowed $1,500, or $10,300. When you eventually sell the replacement shares, the loss comes back.
- The holding period carries over. The clock from your original shares tacks onto the replacement shares, which can turn what looks like a short-term position into a long-term one.
- Nothing illegal happened. A wash sale carries no penalty. It just moves the deduction to a later year. Investors trigger small ones constantly without noticing.
"Substantially Identical" Has Never Been Defined for Funds
Two lots of the same ETF are obviously identical. Beyond that, the IRS has issued no ruling on when two different funds cross the line, and Publication 550 offers only the phrase itself. What exists instead is a practitioner consensus built around one question: do the two funds track the same index?
| Pair | Same index? | Common practitioner view |
|---|---|---|
| VOO ↔ IVV | Yes, both S&P 500 | Risky pair. Same 505 stocks, same weights, near-identical returns. |
| QQQ ↔ QQQM | Yes, both Nasdaq-100 | Risky pair. Same issuer, same index, different share class in all but name. |
| VOO ↔ VTI | No. S&P 500 vs CRSP US Total Market | Widely used swap. 505 stocks vs 3,700+, different index providers. |
| SCHD ↔ VYM | No. Different indexes, different screens | Widely used swap. About 100 holdings vs 500+, meaningfully different portfolios. |
| SPY ↔ RSP | Same stocks, different weighting | Generally viewed as distinct. Equal weight produces materially different returns. |
The logic: funds tracking different indexes hold different securities in different weights and deliver different returns, which is hard to call "identical" in any sense. Funds tracking the same index are economically interchangeable, which is the situation the rule was written to catch. VOO and VTI overlap heavily by weight, but a fund holding 505 stocks and a fund holding 3,700+ from different index providers is the classic harvesting pair for a reason. None of this is settled law. It is the working consensus in the absence of guidance, and a tax professional should confirm whatever pairing you use.
The IRS has had a century to define "substantially identical" and has declined every time. Enforcement actions against investors who swapped between different-index ETFs are essentially unheard of. The practical risk concentrates in same-index pairs and in the cross-account traps below, not in the VOO-to-VTI swap.
The IRA Repurchase Destroys the Loss Permanently
Everything above describes a deferral. One version of the wash sale is worse: selling at a loss in your taxable account and repurchasing in your IRA within the window. Under Revenue Ruling 2008-5, the loss is disallowed and the basis adjustment does not transfer into the IRA. There are no capital gains inside an IRA, so there is no future sale that recovers the deferred loss. A $1,500 disallowed loss in the deferral case comes back later; in the IRA case it is gone. This is the one wash sale outcome that actually costs money rather than timing.
The rule also reaches across accounts generally. You are one taxpayer: a sale in your taxable account and a repurchase in your spouse's account, a joint account, or your Roth IRA all count. Meanwhile, brokers are only required to flag wash sales on identical securities within the same account. A cross-account violation produces a clean-looking 1099-B and an inaccurate tax return, and reconciling that is on you, not the broker.
Dividend Reinvestment Triggers It While You Sleep
Automatic dividend reinvestment is the quiet repeat offender. Sell part of a dividend-paying ETF at a loss, and a scheduled reinvestment of that fund's dividend anywhere in the 61-day window buys "replacement shares," washing the loss on that share count. The amounts are usually small, a few reinvested shares against a much larger sale, but it applies in every account you own the fund in. Anyone harvesting losses in a fund they also hold in an IRA with reinvestment turned on is running the permanent-loss version of this on autopilot. The common fix practitioners suggest is pausing automatic reinvestment around planned sales.
What Deferral Actually Costs: Usually Little, Sometimes Everything
Keeping the earlier numbers: a $1,500 loss disallowed in a taxable account becomes $1,500 of extra basis. If you sell the replacement shares next year, the deduction arrives one tax year late. At a 15% capital gains rate, the cost is a year's delay on roughly $225 of tax savings, which is real but minor. Harvesting losses in a down market mostly survives an accidental wash sale intact.
The two cases that break that comfortable math: the IRA repurchase, where the $225 becomes $0 recovered ever, and losses you needed this year, to offset a large realized gain or to claim the $3,000 annual deduction against ordinary income. Deferral is cheap until the timing was the whole point.
The Wash Sale Rule and ETFs
- The window is 61 days: 30 before the sale, the sale date, and 30 after. Purchases before the loss sale count.
- A disallowed loss in a taxable account is deferred into the replacement shares' basis, not destroyed.
- The IRS has never defined "substantially identical" for funds. Practitioners treat same-index pairs (VOO/IVV, QQQ/QQQM) as risky and different-index pairs (VOO/VTI, SCHD/VYM) as the standard swap.
- Repurchasing in an IRA is the exception that destroys the loss permanently, per Rev. Rul. 2008-5.
- Brokers only flag same-security, same-account wash sales. Cross-account and spousal violations are your job to track.
- Dividend reinvestment inside the window triggers partial wash sales automatically. This is general information, not tax advice.
Common questions
Yes. The wash sale rule under IRC Section 1091 applies to stocks, ETFs, mutual funds, and options on any of them. If you sell an ETF at a loss and buy the same or a substantially identical security within 30 days before or after the sale, the loss is disallowed for that tax year and added to the cost basis of the replacement shares instead. This is general information, not tax advice; confirm your situation with a tax professional.
The IRS has never ruled on it. VOO tracks the S&P 500 (505 stocks) and VTI tracks the CRSP US Total Market Index (3,700+ stocks), so they follow different indexes with different holdings. Many tax practitioners treat funds tracking different indexes as not substantially identical, and this pair is one of the most commonly used swaps in tax-loss harvesting. Two funds tracking the same index, like VOO and IVV, are widely viewed as much riskier to pair. Because there is no formal guidance, confirm your approach with a tax professional.
In a regular taxable account the loss is deferred, not destroyed. The disallowed amount is added to the cost basis of the replacement shares, and the holding period of the original shares carries over. You reclaim the tax benefit when you eventually sell the replacement shares. The exception is repurchasing inside an IRA: under IRS Revenue Ruling 2008-5, the loss is disallowed and there is no basis adjustment, so the deduction is gone permanently.
Yes. The rule looks at you as a taxpayer, not at a single account. Selling at a loss in your taxable account and repurchasing in your IRA, your spouse's account, or a jointly held account can still trigger a wash sale. Brokers are only required to flag wash sales on identical securities within the same account, so cross-account violations will not show up on your 1099-B. Tracking them is your responsibility.
No. Triggering a wash sale is not a violation of any law and carries no penalty. The only consequence is that you cannot deduct the loss in the year of the sale; the loss is deferred into the basis of the replacement shares. Investors trigger small wash sales constantly through dividend reinvestment without ever noticing.