Tax-Loss Harvesting

At its core, harvesting is simple: you sell a position that is worth less than you paid for it, which converts an unrealized (paper) loss into a realized capital loss the IRS recognizes. Until you sell, a decline does nothing for your taxes. Once realized, that loss becomes a number you can use on your return to offset gains and, within limits, income. The subtle part is that the goal is usually not to exit the position permanently but to capture the loss while staying invested through a replacement.

It helps to be clear about what harvesting does and does not do. It does not create free money: it mostly defers tax. When you sell and rebuy a replacement, your new position has a lower cost basis, so a larger gain will eventually be taxed when you sell that. The benefit comes from deferring tax into the future (money kept working longer) and potentially from the rate difference between the ordinary income offset now and a long-term gain later. This is educational framing, not tax advice.

A realized capital loss is used in a specific order. First it offsets your realized capital gains dollar-for-dollar (long-term losses are matched against long-term gains and short-term against short-term first, then netted across). If you have a 10,000 dollar gain and harvest a 10,000 dollar loss, they cancel and there is no capital gains tax on that pair. For the mechanics of gains themselves, see capital gains tax.

If your losses exceed your gains, the leftover net loss can then offset up to 3,000 dollars of ordinary income per year (1,500 dollars if married filing separately). That offset is valuable because ordinary income is often taxed at a higher rate than long-term gains. Anything still unused after that carries forward indefinitely to future tax years, where it can again offset gains and up to the yearly income limit. That is why large harvested losses in a bad market can quietly reduce taxes for years. The 3,000 dollar figure can change, so verify current figures with the IRS or a tax professional.

The point of harvesting is not to time the market by going to cash. If you sell a fund at a loss and it rebounds while you sit on the sidelines, you may lose more to the recovery than you saved in tax. So the standard technique is to sell the loser and immediately buy a similar but not substantially identical replacement, keeping your overall exposure nearly unchanged. A common example is selling one broad US stock index fund and buying a different broad US stock fund that tracks a different index.

The reason "not substantially identical" matters so much is the wash-sale rule, covered next. Two broad-market funds that track different underlying indexes are generally treated as not substantially identical, though this is a genuine gray area and the IRS has not drawn a bright line for funds. Getting the swap right is what lets you bank the loss and stay invested at the same time. Because the "substantially identical" question is a tax-advice question, confirm any specific swap with a tax professional.

Harvesting is exclusively a taxable-account move. Inside a traditional IRA, Roth IRA, or 401k, gains and losses are not taxed as they occur, so a loss there is not deductible and there is nothing to harvest. Selling a loser in a sheltered account gives you no tax benefit at all. The entire value of harvesting comes from the fact that a taxable brokerage account taxes realized gains and lets you deduct realized losses.

There is also a cross-account trap worth flagging: the wash-sale rule reaches across your accounts, including your IRAs and, in many cases, a spouse's account. Selling a stock at a loss in your taxable account and buying the same security in your IRA within the window can disallow the loss, and unlike a normal wash sale, the basis adjustment may effectively be forfeited inside the IRA. So harvesting is not just "only in taxable"; it requires watching your other accounts too. See the wash-sale rule guide. This is general information, not tax advice.

The wash-sale rule is the single biggest thing to get right. It 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 centered on the sale date. If you harvest a loss and rebuy too soon, the IRS simply ignores the loss for now, defeating the whole exercise. The rule exists to stop people from selling only to capture a paper loss while keeping the exact same position.

Importantly, a disallowed loss is not gone: it is added to the cost basis of the replacement shares and their holding period is adjusted, so the benefit is deferred until you eventually sell those. Still, for a harvester the practical goal is to avoid tripping it in the first place, by using a not-substantially-identical replacement and being careful about automatic dividend reinvestment, which can quietly trigger a wash sale. The full mechanics, including what "substantially identical" means and the cross-account reach, live in the dedicated wash-sale rule guide.

Two practical levers shape how much you actually harvest. The first is timing. A loss has to be realized by December 31 to count for that tax year, so year-end is when many investors review positions, but opportunities appear any time a holding falls below cost, and some harvest during market drops through the year rather than waiting. The second is which specific tax lots you sell.

If you bought a holding in several purchases at different prices, each purchase is a tax lot with its own basis. Using specific-lot identification, you can sell the highest-cost lots (the ones with the biggest loss) rather than defaulting to first-in-first-out, which maximizes the harvested loss. Not every broker defaults to this, so it usually has to be set at the time of sale. For the broader menu of tax levers this sits within, see how to reduce investment taxes. Lot choice has real tax consequences, so confirm the mechanics with a tax professional.

The order is fixed: the realized loss cancels capital gains first, then offsets up to the yearly ordinary-income limit, then carries forward indefinitely, and none of it works inside a tax-advantaged account. Harvesting mostly defers tax rather than erasing it, since a lower basis means a larger gain later, but deferral and a favorable rate swap can still be worthwhile. The exact dollar limits and rates change and depend on your circumstances, so treat this as a framework and verify current figures with the IRS or a tax professional. It is not tax advice.

The hard part of harvesting by hand is simply seeing which of your holdings are currently underwater, across every account, and by how much, before the wash-sale calendar closes the window. That is a question about your real positions, not a generic list, which is where an AI assistant that reads across your accounts helps. Walnut, an AI investing app, lets you connect any major US broker, then chat in plain words through Claude, ChatGPT, or its built-in AI to see which holdings are below what you paid and where each one sits. It can surface that context; it does not execute harvests, place trades on its own, or judge wash-sale risk for you. Walnut is not a registered investment adviser or a tax adviser, it does not calculate your taxes, and it does not tell you what to buy or sell. For the AI angle specifically, see tax-loss harvesting with AI.