How to Use Tax-Loss Harvesting to Offset Capital Gains

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Tax-loss harvesting capital gains is the practice of strategically selling investments at a loss to reduce your taxable investment income. According to IRS Topic 409, capital losses must first offset capital gains of the same type before any remaining loss applies to other income. Used correctly, this strategy can meaningfully lower your tax bill without forcing you to abandon your long-term investment plan.

With market volatility running high in 2025, more investors are sitting on unrealized losses they can put to work before year-end. The window to act closes on December 31 — there are no extensions.

How Does Tax-Loss Harvesting Capital Gains Actually Work?

You sell a losing investment, book the loss, and apply it against gains you’ve already realized that year. The IRS requires you to match losses against gains of the same holding-period category first — short-term losses against short-term gains, long-term losses against long-term gains — before crossing categories.

If your total losses exceed your total gains, you can deduct up to $3,000 against ordinary income in that tax year. Any amount beyond $3,000 carries forward to future years with no expiration. This carryforward feature makes tax-loss harvesting valuable even in low-gain years.

After selling, most investors immediately reinvest the proceeds in a similar — but not identical — asset. This keeps portfolio exposure intact while locking in the tax benefit. The key constraint here is the wash-sale rule, which disallows the loss if you repurchase a “substantially identical” security within 30 days before or after the sale.

What Is the Wash-Sale Rule and How Do You Avoid It?

The wash-sale rule, codified under IRC Section 1091, disallows a loss deduction if you buy a substantially identical security within a 30-day window on either side of the sale — a total blackout period of 61 days. The disallowed loss is not gone permanently; it gets added to the cost basis of the repurchased shares.

The rule applies across accounts you control, including IRAs and spousal accounts. Selling a losing stock in your brokerage account and buying it in your IRA the same day triggers the wash-sale rule and kills the deduction.

Permitted Substitutions

Investors typically sidestep the wash-sale rule by replacing a sold fund with a comparable but legally distinct one. For example, selling a Vanguard S&P 500 ETF and buying a Schwab S&P 500 ETF may trigger wash-sale scrutiny because they track the same index. A safer swap involves moving to a broad total-market fund or a different-index ETF that maintains similar market exposure without being “substantially identical.”

Short-Term vs. Long-Term: Does the Loss Type Matter?

Yes — the type of loss determines how much tax value it delivers. Short-term losses offset short-term gains first, which are taxed at ordinary income rates of up to 37% for high earners in 2025. Long-term losses offset long-term gains taxed at preferential rates of 0%, 15%, or 20%, depending on income.

This asymmetry makes short-term losses more tax-efficient, dollar for dollar. A $10,000 short-term loss saving tax at a 32% marginal rate eliminates $3,200 of tax liability. The same $10,000 long-term loss used against a long-term gain taxed at 15% saves only $1,500.

According to IRS Publication 550, once same-type losses are applied, any remaining net loss crosses over to offset gains of the opposite type. Only the net result after all netting can be applied to ordinary income up to $3,000.

When Should You Harvest Losses — and When Should You Wait?

The best time to harvest losses is whenever a position is down enough that the tax savings outweigh transaction costs and the risk of being out of the market for 31 days. There is no requirement to wait until December — proactive mid-year harvesting captures losses before a potential recovery eliminates them.

Many robo-advisors, including Betterment and Wealthfront, run automated tax-loss harvesting daily. Betterment’s research found that daily harvesting can add an estimated 0.77% in after-tax returns annually for taxable accounts, compared to year-end-only harvesting. That advantage compounds significantly over a 20- or 30-year horizon.

You should generally avoid harvesting losses in tax-advantaged accounts like 401(k)s or IRAs. Losses inside these accounts generate no deductible benefit because gains inside them are already tax-deferred or tax-free. Tax-loss harvesting capital gains is exclusively a taxable brokerage account strategy.

If you’re building broader tax efficiency into your financial plan, pairing tax-loss harvesting with strategies like maximizing retirement contributions or deducting home office expenses can compound your annual tax savings meaningfully. And if you’re still working toward the investment surplus needed to harvest meaningful losses, reviewing your financial goals by decade can help prioritize the right moves.

How Do You Report Tax-Loss Harvesting Capital Gains on Your Tax Return?

Capital losses are reported on IRS Schedule D and the supporting Form 8949. Every individual sale goes on Form 8949 with the acquisition date, sale date, proceeds, and cost basis. Schedule D then nets all short-term and long-term transactions to produce a final gain or loss figure.

Your brokerage is required to send a Form 1099-B each February reporting covered transactions with cost basis. However, taxpayers are ultimately responsible for accuracy — especially if you transferred assets between brokers or received shares as gifts, where cost basis tracking may be incomplete.

Carryforward losses are tracked on the Capital Loss Carryover Worksheet inside IRS Schedule D instructions. The amount carries to the following year’s Schedule D automatically if you use tax software like TurboTax or H&R Block. If you file manually, you must transfer the figure yourself each year.

For a broader look at managing your overall tax picture and tracking wealth-building progress over time, it helps to track your net worth regularly — tax-loss harvesting affects both your tax liability and your after-tax investment balance simultaneously. If you’re also navigating employer tax forms or deductions as a self-employed individual, our guide on home office tax deductions covers the reporting process in comparable depth.

Frequently Asked Questions

Can tax-loss harvesting eliminate all my capital gains taxes?

Yes, if your harvested losses equal or exceed your total capital gains for the year, you can reduce your capital gains tax to zero. Any losses beyond your gains can offset up to $3,000 of ordinary income, with the rest carried forward to future years.

Does tax-loss harvesting work in a Roth IRA or traditional IRA?

No. Tax-loss harvesting only applies to taxable brokerage accounts. Losses inside a Roth IRA or traditional IRA are not deductible because those accounts already receive tax-advantaged treatment. Executing the strategy inside a retirement account produces no tax benefit.

What happens to harvested losses I don’t use this year?

Unused capital losses carry forward indefinitely under IRS rules — there is no expiration date. You apply them to gains in future years following the same netting rules: short-term losses offset short-term gains first, long-term losses offset long-term gains first.

How does tax-loss harvesting affect my cost basis going forward?

When you sell a losing position and reinvest in a replacement security, the new position’s cost basis is the price you paid for it. This means if the replacement security also rises in value, you’ll eventually owe capital gains tax on the full appreciation from your new (lower) cost basis — a deferred, not eliminated, tax liability.

Do robo-advisors do tax-loss harvesting automatically?

Yes. Services like Betterment, Wealthfront, and Schwab Intelligent Portfolios offer automated tax-loss harvesting for taxable accounts. They scan for harvestable losses daily and execute trades while managing wash-sale compliance. Some require a minimum account balance to access this feature. If you want to explore these platforms further, our guide to the best robo-advisors for hands-off investing covers current options in detail.

Is tax-loss harvesting worth it for small accounts?

Generally, the benefit diminishes in smaller accounts where transaction costs and the complexity of tracking wash-sale windows may outweigh tax savings. Most financial planners consider the strategy most impactful for taxable accounts above $50,000, though even modest harvesting can add value over time. If you’re still building toward that threshold, focusing on foundational steps like stopping the paycheck-to-paycheck cycle frees up investable capital faster.