Tax-Loss Harvesting: How to Turn Portfolio Losses Into Tax Savings

What Tax-Loss Harvesting Is and Why It Matters

Tax-loss harvesting (TLH) is the practice of selling investments at a loss to offset capital gains taxes. You sell a losing position, claim the loss on your tax return, and immediately buy a similar (but not "substantially identical") investment to maintain your market exposure. You stay fully invested while generating a tax benefit.

The real power of TLH is that the money you would have paid in taxes stays invested and compounds over time. A $10,000 harvested loss that offsets $10,000 of short-term gains in the 24% bracket cuts this year’s tax by $2,400. Against long-term gains it is worth your capital gains rate, and against ordinary income only $3,000 of it can be used each year. That $2,400, invested for 20 years at 7% real return, grows to roughly $9,300. The tax deferral itself generates returns.

TLH is tax deferral with a compounding bonus, not tax elimination. When you eventually sell the replacement investment, your cost basis will be lower, so you will owe taxes on a larger gain. But you have had years or decades of additional compounding on the deferred amount. How much that is worth varies enormously. Vanguard’s research puts the benefit between 0.47% and 1.27% a year on the taxable equity it applies to, and finds investor circumstances drive roughly 60% of the variation. The same harvested loss can be worth fifty times more to one investor than another, depending on the rates involved and how the position eventually ends. We take that number apart in what “tax alpha” actually means.

Calculate Your Tax Savings

Capital Loss Netting: How the IRS Counts Losses

The IRS does not let you simply subtract losses from your income. Capital gains and losses follow specific netting rules on Schedule D of your tax return.

Step 1: Net Within Each Category

Short-term gains and losses (positions held one year or less) are netted against each other. Long-term gains and losses (positions held more than one year) are netted separately.

Step 2: Net Across Categories

If one category has a net gain and the other has a net loss, they offset each other. This is where TLH can be especially valuable: short-term losses can offset short-term gains that would otherwise be taxed at your full marginal income rate (up to 37%).

Step 3: The $3,000 Cap Against Ordinary Income

If your net capital losses exceed your capital gains, you can deduct up to $3,000 per year ($1,500 if married filing separately) against ordinary income. This is a hard cap. If you harvest $50,000 in losses and have no capital gains, you can only use $3,000 this year.

Step 4: Carryforward

Any unused losses carry forward indefinitely to future tax years. Those $47,000 in excess losses from the example above will be available to offset future capital gains, $3,000 per year against ordinary income until fully used. Carryforwards do not expire during your lifetime, but they die with you: your estate cannot use them.

Short-Term vs. Long-Term: The Tax Rate Difference

This rate difference makes TLH particularly valuable when you can use short-term losses to offset short-term gains. Offsetting a gain taxed at 32% saves more than offsetting one taxed at 15%.

The Wash Sale Rule

The wash sale rule is the IRS regulation that prevents you from harvesting a loss and immediately rebuying the same investment. If you sell a security at a loss and buy a “substantially identical” security within 30 days before or after the sale, the loss is disallowed, and the disallowed amount is added to the basis of the replacement shares.¹²

What “Substantially Identical” Means

The statute and the regulation both use the phrase and neither defines it. Publication 550 says it depends on “all the facts and circumstances,” that stock of one corporation is ordinarily not substantially identical to stock of another, and it never mentions mutual funds or ETFs in its wash-sale discussion at all.³ The IRS has issued no ruling on when two funds are substantially identical. Everything past the first rung below is practitioner consensus, which is widely followed and has never been tested.

• Same security. Selling and rebuying the same stock or fund is a wash sale. This is the only rung the rule settles.
• Same fund, different share class. A mutual fund and its own ETF share class (VTSAX and VTI) hold one portfolio. There is no ruling, but practitioners treat them as substantially identical, and this guide does too.⁵
• Same index, different sponsor. Two S&P 500 funds from different companies, or QQQ and QQQM from the same one, hold the same stocks at the same weights. This is the most contested substitution: there is no ruling and tax professionals disagree.⁵ This guide does not recommend it, and the Summitward calculator does not suggest it.
• Different index, same exposure. An S&P 500 fund into a large-cap fund on another index, or VTI into ITOT, which track different index families. This is the common practice, used by advisors and by the robo-advisors that automate harvesting, on the reasoning that different indexes mean different securities.⁶ It has never been ruled on either way.
• Different managers, same factor tilt. Two systematic active funds from different firms targeting the same segment, such as an Avantis fund and its Dimensional counterpart, hold different stocks chosen by different processes and track no index at all, which both issuers state in their prospectuses.⁷⁸ Of the substitutions people make, this is the one furthest from the statute’s language.

Cross-Account Traps

The wash sale rule applies across all your accounts, including your spouse's accounts. Common traps:

• Selling at a loss in your taxable brokerage while your 401(k) auto-purchases the same fund on payday
• Selling at a loss while dividend reinvestment (DRIP) in another account buys the same security within 30 days
• Your spouse buying the same security in their IRA within the 30-day window

The disallowed loss is added to the cost basis of the replacement shares, so in the ordinary case it is deferred until you sell those shares without another wash sale.¹ The exception is a replacement bought inside an IRA. Revenue Ruling 2008-5 disallows that loss and denies the basis increase, so it is gone for good.⁴

Your broker will not catch most of this. Form 1099-B reports a disallowed wash-sale loss only when the replacement has the same CUSIP and was bought in the same account. Publication 550 adds that you cannot deduct a wash-sale loss even if the form does not report it, so cross-account and different-fund washes are yours to track.³

Replacement Fund Strategy

The key to effective TLH is having pre-planned replacement funds that maintain your target asset allocation while avoiding wash sale issues. You want investments that give you similar market exposure (so your portfolio stays on track) but are not substantially identical to what you sold.

Common Replacement Pairs

Every pair tracks a different index. The S&P 500 fund maps to a large-cap fund on another index rather than to another S&P 500 fund, because two funds on one index are the most contested substitution; Schwab’s SCHX, on the Dow Jones large-cap index, works the same way. The Avantis and Dimensional pairs are the strongest substitutions on the list: different managers, different holdings, and no index for either to share. One trap inside that lineup: AVGV is a fund of funds that holds AVUV, AVLV, AVIV, AVDV and AVES directly, so it is the wrong replacement for any of them. Index names and fund names as stated by the issuers and their SEC filings on September 7, 2026.

The strategy is straightforward: sell the primary holding at a loss, immediately buy the replacement to maintain exposure, wait at least 31 days, then optionally swap back to your primary holding if you prefer it. The swap-back resets your holding period for the position.

When TLH Is Worth It (and When It Is Not)

TLH Is Most Valuable When:

• You have a long time horizon. The longer the deferred taxes stay invested, the more the compounding benefit accumulates. A 30-year-old investor benefits more than a 60-year- old.
• You are in a high tax bracket now and expect a lower bracket later. Deferring gains from a 35% bracket to a 15% bracket in retirement is a permanent tax rate arbitrage, not just deferral.
• You have large capital gains to offset. Selling concentrated stock (RSU vests, company stock, real estate) creates gains that harvested losses can offset dollar for dollar.
• Markets are volatile. Down markets create the most harvesting opportunities. The 2020 COVID crash and 2022 bear market were excellent TLH environments.

TLH Has Limited Value When:

• Your portfolio is mostly in tax-advantaged accounts. TLH only works in taxable accounts. Gains in a 401(k) or IRA are already tax-deferred.
• The loss is small relative to transaction friction. Harvesting a $200 loss to save $48 in taxes may not be worth the effort and tracking complexity.
• You expect to be in a higher tax bracket when you realize the gains. If your future rate is higher than your current rate, deferral can increase your lifetime tax bill.

Two exits make harvesting worth more. If you eventually donate the replacement shares to charity, or hold them until death so your heirs receive a stepped-up basis, the lower basis the harvest created is never taxed. The deferral becomes permanent.

Worked Example: Tax Benefit Calculation

Alex has a taxable portfolio of $200,000. After a market downturn, one position has an unrealized loss:

• Vanguard Total Stock (VTI): purchased for $80,000, now worth $65,000 (unrealized loss of $15,000)
• Alex is in the 32% federal bracket and 5% state bracket (37% combined marginal rate)
• Alex has $8,000 in short-term capital gains from RSU sales this year

Step 1: Harvest the Loss

Alex sells VTI for $65,000, realizing a $15,000 long-term capital loss. Alex immediately buys $65,000 of Schwab U.S. Broad Market (SCHB) to maintain total market exposure.

Step 2: Apply the Loss

Step 3: Calculate the Tax Savings

The remaining $4,000 in carryforward losses will offset future gains. At the same tax rate, that is an additional $1,480 in future tax savings, plus compounding on the deferred amount in the meantime.

Step 4: Understand the Tradeoff

Alex's SCHB position now has a cost basis of $65,000 instead of the original $80,000 VTI basis. When Alex eventually sells SCHB, the gain will be $15,000 larger. But Alex has had the use of that $4,070 in tax savings for years, generating additional returns. Over a 20-year holding period at 7% real return, that $4,070 grows to roughly $15,750, more than offsetting the deferred tax.

Related Guides

Tax-loss harvesting is one piece of a tax-aware investment strategy. Related reading:

• What a $16,364 Rental Write-Off Is Actually Worth separates a tax loss from an economic one, and prices rental depreciation against the passive-activity limits.
• Yes, an Unrealized Loss Is Still a Loss takes apart “it’s not a loss until you sell,” the belief that stops most people harvesting in the first place.
• What “Tax Alpha” Actually Means prices a harvested loss under every exit and takes apart the 1% claim, with a calculator for your own numbers.
• Do You Actually Need Direct Indexing? whether a paid harvesting service earns its fee over doing this yourself with a couple of funds.
• How to Sell Tax-Efficiently: SpecID and Tax Lots pairs lot selection with harvesting and covers FIFO vs HIFO vs MinTax, with a lot-method calculator.
• If Dimensional Gets Sold, Should Factor Investors Care? uses harvested losses to lower the tax cost of switching out of an appreciated bespoke ETF, with a switching-cost calculator.
• Tax-Aware Long-Short: Real Tax Alpha or Marketing? is the long-short / SMA / HNW companion to this post: how leveraged TALS strategies extend loss capacity beyond the ~30% ceiling of long-only direct indexing, plus a hurdle calculator and the Section 1259 caveat.
• RSU Tax Strategy addresses the tax impact of employer stock vests and when TLH can offset the income from selling appreciated shares.
• Concentration Risk covers when a single position dominates your portfolio and how to diversify while using TLH to manage the tax cost.
• Roth Conversion Ladder explains another tax optimization strategy for early retirees, complementing TLH in taxable accounts.
• Safe Withdrawal Rate shows how tax-efficient withdrawals improve your effective spending rate in retirement.

Key Takeaways

• TLH is tax deferral, not elimination. You pay taxes later on a lower cost basis, but the deferred amount compounds in your portfolio. For long-horizon investors, the compounding benefit is substantial.
• The wash sale rule has a 61-day window. You cannot buy a substantially identical security 30 days before or after the loss sale. The rule applies across all your accounts, including your spouse's.
• Use pre-planned replacement pairs. Have a list of different-index funds ready (VTI to ITOT, VOO to VV, AVUV to DFSV) so you can harvest quickly during downturns without disrupting your allocation. Two funds on one index are the most contested substitution, and the IRS has never ruled on funds at all.
• Short-term loss offsets are most valuable. Short- term gains are taxed at ordinary income rates (up to 37%). Using losses to offset short-term gains saves more per dollar than offsetting long-term gains (taxed at 0-20%).
• Harvest proactively in down markets. Do not wait until year-end. Monitor your portfolio during market downturns and harvest losses when they appear. Losses can vanish quickly in a recovery.
• TLH only works in taxable accounts. Gains and losses in 401(k)s, IRAs, and other tax-advantaged accounts are irrelevant for TLH purposes. Focus your harvesting on your taxable brokerage.

Sources

1. 26 U.S.C. §1091(a) and (d), the wash-sale statute (61-day window; disallowed loss added to the basis of the replacement). law.cornell.edu
2. Treas. Reg. §1.1091-1(a) and (f) (the 61-day period; contracts and options to acquire; no definition of “substantially identical”). law.cornell.edu
3. IRS Publication 550 (2025), revised March 5, 2026, “Wash Sales,” pages 86 to 88 (facts and circumstances; stock of different corporations ordinarily not substantially identical; no mention of funds; Form 1099-B box 1g limited to same CUSIP and same account; loss disallowed whether or not reported). irs.gov (PDF)
4. Rev. Rul. 2008-5, 2008-1 C.B. 271 (loss disallowed when the replacement is bought in an IRA; no basis increase under §1091(d)). irs.gov (PDF)
5. Bogleheads wiki, “Wash sale,” revised August 1, 2026 (secondary, community-maintained: no ruling on same-index funds from different sponsors, experts differ; share classes of one fund “probably substantially identical”). bogleheads.org
6. Ben Henry-Moreland, Kitces.com, “Tax-Loss Harvesting Best Practices,” September 7, 2022 (secondary, practitioner: the IRS is “notably vague” on funds; different-index replacement used by many advisors and by robo-advisors). kitces.com
7. American Century Investments, Avantis U.S. Small Cap Value ETF summary prospectus (Form 497K), filed December 31, 2025 (“an actively managed exchange-traded fund (ETF) that does not seek to replicate the performance of a specified index”; expense ratio 0.25%). The other Avantis funds in the table carry the same language in their own filings. sec.gov
8. Dimensional Fund Advisors, Dimensional US Small Cap Value ETF summary prospectus (Form 497K), filed February 27, 2026 (“does not seek to replicate the performance of a specific index”; expense ratio 0.30%). The other Dimensional funds in the table carry the same language in their own filings. sec.gov