Every investor eventually owns something that went down. Tax-loss harvesting is the disciplined practice of turning those paper losses into something useful: a reduction in your tax bill. By selling investments at a loss and using those losses to offset taxable gains — and even some ordinary income — you keep more of what you earn. Done correctly, it is one of the few strategies that can improve after-tax returns without requiring you to predict the market.
Table of Contents
- What Tax-Loss Harvesting Is
- How It Works: A Worked Example
- The Wash-Sale Rule: The Trap to Avoid
- Limits, Carryforwards, and Ordinary Income
- Who Benefits Most
- Common Mistakes
- Key Takeaways
What Tax-Loss Harvesting Is
When you sell an investment for more than you paid, the profit is a capital gain, and the IRS generally taxes it. When you sell for less than you paid, the difference is a capital loss. Tax-loss harvesting is the strategy of deliberately realizing losses — selling positions that are underwater — so those losses can offset gains elsewhere in your portfolio, reducing the taxes you owe.
Crucially, an unrealized loss does nothing for your taxes. A stock sitting in your account down 30 percent generates no tax benefit until you sell it. Harvesting converts the invisible loss into a recognized one the tax code acknowledges. You do not have to abandon the investment thesis, either: you can immediately buy a similar (but not “substantially identical”) asset to keep your portfolio positioned the way you want it.
The strategy applies to taxable brokerage accounts. It has no effect inside 401(k)s, traditional and Roth IRAs, or other tax-advantaged accounts, where gains and losses are not taxed annually in the first place. Harvesting is therefore a tool for the taxable portion of your portfolio — which, for many investors, grows increasingly important as wealth accumulates outside retirement accounts.
How It Works: A Worked Example
Imagine you bought shares of a tech ETF for $20,000 and they are now worth $14,000 — a $6,000 unrealized loss. Earlier this year you sold another holding for a $6,000 gain. Without harvesting, you owe capital gains tax on the full $6,000 profit. If instead you sell the underwater ETF, the $6,000 loss cancels the $6,000 gain, and your net taxable gain is zero. You have legally erased the tax bill.
To stay invested, you then buy a similar-but-different fund — say, swapping one broad large-cap ETF for another tracking a comparable index. Your market exposure is nearly unchanged, but you have banked a tax asset. Your new cost basis is lower ($14,000 instead of $20,000), which means a larger taxable gain if you later sell at a profit — harvesting defers taxes more often than it permanently eliminates them. But deferral has real value: money not sent to the IRS today keeps compounding for you.
The benefit scales with your tax bracket. Offsetting a short-term gain (taxed as ordinary income, potentially at high marginal rates) is worth more per dollar than offsetting a long-term gain (taxed at preferential rates). Sophisticated harvesters therefore prioritize realizing losses against short-term gains first. This interplay with capital gains tax brackets is where the real planning happens, and it connects to broader questions about how tax policy shapes investor behavior.
The Wash-Sale Rule: The Trap to Avoid
The IRS anticipated the obvious abuse — selling at a loss and instantly rebuying the same security — and created the wash-sale rule to stop it. If you sell a security at a loss and buy a “substantially identical” security within 30 days before or after the sale (a 61-day window), the loss is disallowed for current tax purposes. Instead, the disallowed loss is added to the cost basis of the replacement shares, deferring the benefit rather than destroying it entirely — but the immediate deduction you wanted is gone.
“Substantially identical” is deliberately fuzzy. Selling one S&P 500 index fund and buying a different company’s S&P 500 index fund is widely considered acceptable — different securities tracking the same index. Selling shares of Apple and immediately rebuying Apple is clearly a wash sale. Options, and even purchases inside your IRA, can trigger the rule: buying the same stock in your IRA within the window also disallows the loss in your taxable account, a trap that catches many investors.
The practical defense is a replacement-security plan made before you sell. Identify the substitute fund or stock in advance, execute both legs deliberately, and calendar the 31-day mark. Automated harvesting features in robo-advisors handle this systematically, but do-it-yourself investors need the same discipline. IRS Publication 550 discusses wash sales in detail on irs.gov.
Limits, Carryforwards, and Ordinary Income
Capital losses first offset capital gains of the same type, then gains of the other type (short-term losses offset short-term gains first, then long-term gains). If your losses exceed your gains, you can deduct up to $3,000 of the excess against ordinary income each year ($1,500 if married filing separately) — a modest but valuable direct reduction of your tax bill.
Unused losses do not vanish: they carry forward indefinitely to future tax years. An investor who harvests a large loss in a brutal market year can deploy it against gains for years afterward. This makes bear markets paradoxically productive for taxable investors — the deeper the unrealized losses, the richer the harvest, provided you act before year-end and respect the wash-sale window.
State taxes add another layer. Most states follow the federal treatment of capital losses, but rules and limits vary, and a few states handle carryforwards differently. If you live in a high-tax state, the combined federal-plus-state value of a harvested loss can be substantial — another reason to model the strategy with your actual marginal rates rather than rules of thumb.
Who Benefits Most
High earners in high tax brackets gain the most in absolute dollars, since each harvested dollar offsets income taxed at their steep marginal rate. Active rebalancers benefit too: anyone regularly trimming winners to maintain an asset allocation generates gains that need offsetting, and harvesting supplies the losses to do it.
Investors with concentrated positions — founders with company stock, employees with RSUs — can use harvested losses from the diversified part of their portfolio to soften the tax impact of gradually selling the concentrated holding. And retirees managing Roth conversions or Medicare premium thresholds can time harvesting to fine-tune taxable income in a given year.
Who benefits least? Investors whose wealth sits entirely in retirement accounts, very small portfolios where trading costs and complexity outweigh the savings, and anyone in the 0 percent capital-gains bracket — if you owe no tax on gains, there is nothing to offset. As with any strategy involving small-business owner finances, the right answer depends on your full picture, not the tactic in isolation.
Common Mistakes
The classic mistake is letting the tax tail wag the investment dog: selling a solid long-term holding purely for the loss, then watching the replacement underperform or drifting from your target allocation. Harvesting should never change what you own in any meaningful way — if it does, you are trading, not harvesting.
Second, forgetting the wash-sale window across accounts. Dividend reinvestment plans are the silent killer here: an automatic reinvestment of a dividend within 30 days of your harvest sale can trigger a partial wash sale without you lifting a finger. Turn off automatic reinvestment on securities you plan to harvest, or use the distributions as cash.
Third, harvesting in December without a plan. Year-end scrambles lead to sloppy substitute choices and missed windows. The best practitioners review unrealized losses quarterly, harvest opportunistically during volatility, and treat December as a final check rather than a starting gun. Finally, keep meticulous records — dates, amounts, substitute securities, and carryforward balances — because the IRS expects you to substantiate every dollar, and brokerage 1099s do not always tell the full story.
