Tax-loss harvesting without the hype
By Luigi PooleUpdated
Realizing a loss in a taxable account offsets capital gains dollar for dollar, then up to $3,000 of ordinary income, with the rest carried forward. But the replacement position's basis resets lower, so most of the benefit is deferral — worth having, worth not overstating.
Tax-loss harvesting is one transaction with one consequence: you sell something in a taxable brokerage account for less than you paid, converting a paper loss into a realized capital loss the tax code will let you use. That loss nets against realized capital gains dollar for dollar. If losses exceed gains, up to $3,000 a year comes off ordinary income — a flat amount that has never been indexed to inflation — and anything still unused carries forward with no expiry date.
What the pitch usually leaves out is the second half. You take the proceeds and buy something similar, so the portfolio keeps roughly the same exposure, but the new position carries a lower cost basis. A lower basis means a larger gain the day you eventually sell. The tax you avoided this year is, in most cases, a tax you moved rather than a tax you escaped, and everything worth knowing about harvesting comes down to how much that move is worth and what it costs to make.
What the loss actually offsets
Gains and losses sort into two buckets before anything else happens. Short-term covers positions held a year or less and is taxed at your ordinary rate. Long-term covers everything held longer and gets the preferential capital gains rates. Losses net inside their own bucket first — short against short, long against long — and only the surviving figures cross over to cancel each other.
That ordering is why a short-term loss is the more valuable object. It attacks short-term gains first, which are the expensive ones, while a long-term loss can only reach them after the long-term side has been cleared. Character survives a carryforward as well: a short-term loss you cannot use this year arrives next year still short-term, still aimed at the higher rate.
Once gains are exhausted, the remaining loss meets a hard ceiling — $3,000 against ordinary income per year, half that if you file separately from a spouse. A $40,000 loss with no gains to absorb it therefore takes more than a decade to spend at that rate, which is the practical argument against treating one large harvest as a windfall. The excess is not lost. It queues.
A harvest, end to end
Say you sold a concentrated stock position earlier in the year for a $20,000 long-term gain. A fund you bought for $60,000 is now worth $46,000. You sell it, book the loss, and move the full $46,000 into a fund tracking a different index the same afternoon. Assume a 15% long-term rate.
| This year | Do nothing | Harvest the loss |
|---|---|---|
| Long-term gain realized | $20,000 | $20,000 |
| Long-term loss realized | — | $14,000 |
| Net gain taxed | $20,000 | $6,000 |
| Tax at 15% | $3,000 | $900 |
| Basis of the fund you now hold | $60,000 | $46,000 |
So $2,100 stays in the account. Now run it forward. Both versions hold $46,000 of broadly the same market exposure; suppose it is worth $60,000 when you finally sell.
| At the eventual sale | Do nothing | Harvest the loss |
|---|---|---|
| Proceeds | $60,000 | $60,000 |
| Cost basis | $60,000 | $46,000 |
| Gain realized | $0 | $14,000 |
| Tax at 15% | $0 | $2,100 |
The same $2,100, handed back. Nothing was erased. What the harvest bought was the use of $2,100 in the meantime — an interest-free loan from the Treasury whose repayment date you get to choose.
So what is the benefit, honestly
Three things make that loan worth taking. The first is time: the $2,100 compounds while the bill at the end sits still, so the whole return on the maneuver is whatever the deferred money earns before it is repaid.
| What deferring $2,100 of tax is worth, after repaying it | |
|---|---|
| 5 years | ≈ $710 |
| 10 years | ≈ $1,661 |
| 20 years | ≈ $4,635 |
| 30 years | ≈ $9,961 |
Assumes the $2,100 stays invested at 6% a year and the deferred bill is still $2,100 when it comes due. Bars show what is left after paying it.
Five years of it is worth a few hundred dollars — real, but not a strategy. Thirty years is a different number entirely, and it is the same compounding that governs everything else in the account, applied to a smaller sum over a longer runway.
The second is rate arbitrage, and this part is not deferral at all. A short-term loss deducted against a 32% ordinary rate today, repaid later as a long-term gain taxed at 15%, is a permanent seventeen-point gain on that amount. Harvesting short-term losses while your future gains are long-term is where the genuine, non-refundable money is.
The third is the set of exits that cancel the bill outright. Heirs receive a step-up in basis, so a deferred gain carried to the end is never taxed. Appreciated shares given to charity are never sold by you. And a low-income year that drops your long-term gains into the 0% bracket lets you realize the deferred gain for nothing. Deferral becomes elimination only if one of those three actually happens — which is why harvesting rewards people who know what the position is eventually for.
It is also why the marketing figure of "1 to 2% a year in tax alpha" should be read as front-loaded rather than perpetual. Harvestable losses are abundant in the first years after funding an account and after a drawdown, then grow scarce as basis falls further below value. A twenty-year average hides a curve that is steep at the start and nearly flat later. Run your own holding period and contribution rate through compound growth before deciding what the benefit is worth to you.
Run your numbersCompound growthThe wash-sale rule
You cannot deduct the loss if you buy the same or a substantially identical security within 30 days before or after the sale. The window runs in both directions, so it is 61 days wide with the sale in the middle, and a purchase made in the month before you sold counts just as much as one made after.
A wash sale is not a penalty. The disallowed loss is added to the basis of the replacement shares and the old holding period tacks on, so the deduction returns when the replacement is sold. It is a delay, which is worth remembering before anyone panics about one.
Two versions do real damage. The first is the retirement account: buy the replacement inside an IRA — a rollover, a Roth, one funded through the backdoor — and the disallowed loss has no taxable basis to attach to, so it disappears permanently. Automatic investing on a schedule you set years ago is the usual culprit, and the cleanest defense is to never hold the same fund in both a taxable and a retirement account.
The second is scope. The rule follows the taxpayer, not the account. A spouse's purchases count. A company you control counts. Dividend reinvestment counts, including the small automatic ones nobody thinks of as a purchase. Options and warrants on the same underlying count too. Brokers reconcile wash sales only within a single account, so a clean tax form is not evidence of a clean year.
Picking a replacement that is similar but not identical
"Substantially identical" has never been defined for funds, which leaves everyone working from practice rather than rule. Swapping between two funds that track the same index from different issuers is the common approach and also the unresolved one. The conservative version changes the index itself: a total-market fund in place of a large-cap one, a broad international fund in place of a developed-markets one. The exposure stays close, the tracking difference is small over any horizon that matters, and the position needs no argument.
Sitting in cash for 31 days is the other route, and the poorest one for money meant to stay invested. Market returns arrive in a small number of days that nobody schedules; buying back after a rebound has cost more than one harvest was ever worth.
One setting decides whether any of this works cleanly: your broker's cost-basis method. Average cost or first-in-first-out will choose lots for you, and will regularly choose the wrong ones. Specific identification lets you sell only the lots that are underwater and leave the profitable ones untouched. Set it before you need it, because it usually cannot be applied after the trade.
When it is not worth doing
Skip it when your long-term rate is already 0% — a loss spent against a gain taxed at nothing buys nothing, and that year is better used deliberately realizing gains to reset basis upward. Skip it when the loss is small, since a few hundred dollars of deduction does not justify a spread, a trade, and a year of record-keeping. Skip it on anything thinly traded, where the round trip costs real money. And skip it when the replacement is a fund you would not otherwise own: a higher fee or a worse index compounds against you far longer than the tax saving compounds for you.
The underlying pattern is a familiar one — accept small friction now to move a bill later, then arrange for the bill never to arrive. The receipt strategy that turns a health account into a long-term investment is the same shape, and it fails the same way if the last step is never taken.
Common follow-ups
Does the wash-sale rule apply across my accounts?
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Yes. It follows the taxpayer, not the account. A purchase in your spouse's brokerage, a joint account, or a company you control triggers it, and so does an automatic dividend reinvestment you forgot was switched on. Brokers only report wash sales within one account, so the tracking is yours.
What happens if I buy the replacement in my IRA?
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The loss is disallowed and, unlike an ordinary wash sale, it is gone for good. There is no taxable basis in a retirement account to add it to, so the deduction simply vanishes. Set your retirement accounts' automatic investing to something you never hold in a taxable account.
Is swapping one S&P 500 fund for another safe?
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Not clearly. Two funds tracking the identical index, from different issuers, sit in a gray area the tax code has never defined for funds. The conservative practice is to change the index itself — a total-market fund for a large-cap one — so the holdings genuinely differ rather than merely the ticker.
How much unused loss can I carry forward?
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All of it, indefinitely, until death. Losses beyond your gains offset up to $3,000 of ordinary income a year, and whatever remains rolls forward with its short-term or long-term character intact. Carryforwards do not pass to heirs, which is an argument for realizing gains against a large balance rather than hoarding it.
Can I harvest losses in my 401(k)?
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No. Gains and losses inside a tax-deferred or tax-free account have no tax consequence, so there is nothing to realize. Harvesting is a taxable-brokerage activity only, which is one reason a large taxable account changes how the rest of the portfolio should be arranged around it.