Tax-Loss Harvesting: How to Lower Your Tax Bill With Investment Losses

Tax-loss harvesting is the practice of selling investments at a loss inside a taxable brokerage account to offset realized capital gains and reduce your tax bill. Done correctly, it lowers the annual tax drag on a portfolio, and for retirees and pre-retirees it can coordinate with Roth conversion planning and MAGI management. This guide covers the mechanics, the 2026 rules and limits, the wash-sale trap, and the year-end deadline.

Last reviewed: August 2026 | Written and reviewed by Craig Wear, CFP®, founder of Q3 Advisors

How Tax-Loss Harvesting Works

Tax-loss harvesting works in three steps: realize the loss, apply it against gains, and reinvest in a similar but not identical asset to stay invested. The loss offsets capital gains dollar for dollar, and any net loss beyond gains deducts up to $3,000 against ordinary income (IRC §1211(b)). The wash-sale rule is the main constraint on step three.

1. Realize the loss. Sell a position in your taxable account that is worth less than what you paid for it, which converts a paper loss into a realized capital loss the IRS recognizes.
2. Offset your gains. Apply the realized loss against capital gains elsewhere in the portfolio. If losses exceed gains, up to $3,000 ($1,500 if married filing separately) reduces ordinary income, and the rest carries forward.
3. Reinvest in a similar asset. Buy a related but not substantially identical fund so you keep your market exposure and target allocation without triggering the wash-sale rule.

The $3,000 Deduction and Indefinite Carryforward

When capital losses exceed capital gains, tax-loss harvesting lets you deduct up to $3,000 of the net loss against ordinary income each year ($1,500 if married filing separately), per IRC §1211(b). Losses above that cap carry forward to future tax years with no expiration. The $3,000 figure has been fixed since 1978 and is not indexed to inflation.

Because the cap is frozen in nominal dollars, its real value keeps eroding. A $3,000 deduction for a taxpayer in the 2026 24% bracket (which runs up to $201,775 of taxable income for single filers) offsets a modest amount of tax, so the larger prize for high-net-worth investors is banking carryforward losses to deploy against big gains in a future year. Those stored losses can cushion a large sale or a spike in realized gains later.

The Wash-Sale Rule (IRC §1091)

The wash-sale rule (IRC §1091) disallows a loss if you buy the same or a substantially identical security within 30 days before or after the sale, a 61-day window counting the trade day. The disallowed loss is not erased in a taxable account: it is added to the cost basis of the replacement security and deferred until you sell that position.

The rule applies across all your accounts, including IRAs, 401(k)s, and a spouse’s accounts, which is why a coordinated view matters. Automatic dividend reinvestment inside the window can also trip the rule, so many investors pause reinvestment on positions they are actively harvesting. The IRS has never fully defined substantially identical, so the practical approach is to swap into a fund that tracks a different index. The table below shows how that can look.

Fund choices here are neutral illustrations, not recommendations. Whether two securities are substantially identical can depend on facts you should confirm with a tax professional.

Only Taxable Accounts Qualify (and the Costly IRA Mistake)

Tax-loss harvesting applies only to taxable brokerage accounts. Gains and losses inside an IRA or 401(k) have no current tax effect because those accounts are already tax-sheltered, so a loss realized there produces no deduction. The efficiency strategy for retirement accounts instead centers on withdrawal sequencing, Roth conversions, and long-term bracket management.

There is a costly wash-sale nuance most explainers omit. If you sell at a loss in a taxable account and repurchase a substantially identical security inside your IRA within the 61-day window, the loss is permanently disallowed. IRA cost basis cannot be adjusted, so the “add the loss to the replacement’s basis” mechanic that normally defers the loss does not apply, and the deduction disappears for good. Keep harvesting trades and IRA buys clear of one another.

Short-Term vs Long-Term Losses and 2026 Capital-Gains Rates

The IRS separates short-term losses (assets held one year or less) from long-term losses (held more than one year). Short-term losses first offset short-term gains, which are taxed as ordinary income up to 37%. Long-term losses first offset long-term gains, taxed at 0%, 15%, or 20%. Netting short-term losses against short-term gains often produces the largest benefit.

Excess short-term losses can then offset long-term gains, and excess long-term losses can offset short-term gains. The 2026 long-term capital-gains thresholds (IRS Rev. Proc. 2025-32) are shown below.

The Year-End Deadline: Trade by Late December

The deadline for tax-loss harvesting is the last trading day of the calendar year, December 31, 2026. To realize a loss for a given tax year, the sale must be executed by year-end. Since US securities moved to T+1 settlement on May 28, 2024, trades settle one business day later, so many practitioners place harvesting sales by the second-to-last business day of December to be safe.

Waiting until the final hours of December is risky because holiday schedules, order queues, and settlement timing can push a transaction past the line. Investors who monitor portfolios throughout the year, rather than only at year-end, tend to capture more temporary dips when individual holdings decline even in an overall rising market.

The 3.8% NIIT Double Benefit for High Earners

For high earners, tax-loss harvesting can deliver a second layer of savings through the Net Investment Income Tax. The NIIT adds 3.8% on net investment income once modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly). Because harvesting reduces net capital gains, it can trim both the regular capital-gains tax and the extra 3.8% at the same time.

That combined effect is why the strategy is often more valuable for investors already over the NIIT thresholds than a simple bracket comparison suggests. To see how the surtax is calculated and which income counts, review our overview of the Net Investment Income Tax for 2026.

Coordinating Tax-Loss Harvesting With Your Retirement Tax Plan

Tax-loss harvesting is most useful as one piece of a retirement tax plan, not a standalone move. A Roth conversion produces ordinary income, so realized capital losses do not directly offset the conversion beyond the $3,000 ordinary-income allowance. They can, however, offset other capital gains in the same year, which lowers MAGI and can create room within a target bracket.

Reducing realized gains also helps manage MAGI for IRMAA, the Medicare surcharge that begins above $109,000 (single) or $218,000 (joint) MAGI on a two-year lookback. Coordinating these levers is where planning value concentrates. Many investors weigh harvesting alongside Roth conversion strategy, questions of how much to convert to a Roth, and the timing of required minimum distributions in 2026.

One caveat cuts the other way. If you plan to hold an appreciated position until death, heirs generally receive a step-up in basis that can erase the embedded gain, so realizing a small loss today may forfeit more value than it saves. The break-even math on conversions follows a similar logic: the right choice depends on time horizon, future brackets, and estate goals.

Is Tax-Loss Harvesting Worth It?

Tax-loss harvesting can be worthwhile for investors with meaningful taxable balances, and its value rises for those subject to the 3.8% NIIT. The core benefit is deferral, not permanent elimination: reinvesting at a lower basis means a larger gain can surface later. The guiding principle is not to let the tax tail wag the dog.

Sound tax reasons should never override a sensible investment plan. Harvesting a tiny loss that triggers portfolio drift, higher trading friction, or a wash-sale error can cost more than it saves. Weighed inside a coordinated plan that considers your bracket, carryforward balance, and estate intentions, it can be a durable contributor to after-tax outcomes over time.

Frequently Asked Questions

How much can you write off with tax-loss harvesting?

Tax-loss harvesting can offset an unlimited amount of realized capital gains, plus up to $3,000 of ordinary income per year ($1,500 if married filing separately) under IRC §1211(b). If your net loss exceeds $3,000, the remainder carries forward to future tax years indefinitely until it is used against gains or the annual ordinary-income allowance.

Is tax-loss harvesting really worth it?

Tax-loss harvesting can be worth it for investors with sizable taxable brokerage accounts, and especially for high earners subject to the 3.8% Net Investment Income Tax. The benefit is a deferral of tax rather than permanent elimination, so its value depends on your bracket, portfolio size, and whether you intend to hold positions until death for a step-up in basis.

What is the downside of tax-loss harvesting?

The main downside is that tax-loss harvesting defers tax rather than erasing it: reinvesting at a lower cost basis means a larger gain may surface later. Other drawbacks include wash-sale errors, gradual portfolio drift from repeated swaps, transaction friction on small losses, and forfeited step-up-in-basis value on positions you would have held until death.

Can you tax-loss harvest in an IRA or 401(k)?

No. Tax-loss harvesting applies only to taxable brokerage accounts. Gains and losses inside an IRA or 401(k) carry no current tax consequence. Worse, if you repurchase a substantially identical security inside an IRA within the wash-sale window, the loss is permanently disallowed, because IRA basis cannot be adjusted and the deferred-loss mechanic does not apply.

When is the deadline for tax-loss harvesting?

The deadline is the last trading day of the year, December 31, 2026. Because US securities settle one business day after the trade (T+1, effective May 28, 2024), many practitioners execute harvesting sales by the second-to-last business day of December so the transaction is complete and counts within the tax year.

What counts as a substantially identical security?

The IRS has never fully defined substantially identical under IRC §1091. In practice, most advisers treat two funds tracking the same index (for example, VOO and IVV, which both follow the S&P 500) as risky, while funds tracking different indexes (an S&P 500 fund versus a total-market fund) are generally viewed as different enough to avoid a wash sale.