Tax-gain harvesting: the 0% bracket most investors never use

Most investors know about tax-loss harvesting: selling losers to bank a deduction. Far fewer know its mirror image. The US tax code has a 0% federal rate on long-term capital gains for taxpayers below a surprisingly high income threshold — and in any year you're under it, you can sell winners, pay literally nothing in federal tax on the gains, and immediately buy the shares back at a higher cost basis. It's called tax-gain harvesting, and for people with low-income years — early retirees, grad students, sabbatical takers, career changers — it's free money hiding in plain sight.

The 0% bracket, concretely

Long-term capital gains (assets held over a year, in a taxable account) are taxed at 0%, 15%, or 20% depending on your taxable income. For 2025, the 0% rate applies up to roughly $48,350 of taxable income for singles and about $96,700 for married filing jointly — and that's AFTER the standard deduction (about $15,000 single / $30,000 joint). Add those together and a married couple can have roughly $126,000 of gross income, including the gains themselves, and still pay 0% federal tax on long-term gains filling the bracket. The gains 'stack' on top of your ordinary income, so the harvestable amount is the gap between your other taxable income and the threshold.

Why you'd bother: the basis reset

When you sell a winner and rebuy it, your cost basis resets to the new, higher price. Every dollar of gain you harvested at 0% is a dollar you will never pay 15% on later. Crucially, the wash-sale rule — the 30-day repurchase restriction that complicates loss harvesting — applies ONLY to losses. There is no wash-GAIN rule. You can sell at 10:01 and rebuy the identical fund at 10:02, keeping your portfolio exactly the same while permanently erasing embedded gains.

Who has the low-income years for this

• Early retirees in the gap years between quitting work and starting Social Security or required minimum distributions — the classic use case, often repeatable annually for a decade.
• Anyone with a sabbatical, layoff year, unpaid leave, grad school stint, or business startup year with unusually low income.
• Young investors and residents early in their careers who hold appreciated taxable investments before the big salaries arrive.
• Parents note: harvesting in a CHILD'S custodial account works too, but kiddie-tax rules tax a child's investment income above ~$2,700 at the parents' rate — so the harvestable amount per kid is small.
• Retirees deciding between Roth conversions and gain harvesting in the same low-income space — you usually can't max both; conversions fill the bracket with ordinary income that pushes gains upward. Run both scenarios; conversions often win if RMDs loom large, harvesting wins if taxable gains dominate your balance sheet.

The December routine

1. In early December, estimate your taxable income for the year: wages, interest, dividends (including the fund distributions announced for late December), minus your deduction.
2. Compute your headroom: the 0%-bracket ceiling minus taxable income. That's your maximum harvest.
3. Pick taxable-account lots with long-term gains (verify the holding period — short-term gains are ordinary income and don't qualify) and sell up to the headroom, using specific-lot identification.
4. Rebuy the same or equivalent fund immediately if you want the portfolio unchanged — no waiting period applies to gains. This is also a free chance to fix old mistakes: exit that overpriced legacy fund at 0% and buy the index fund you actually want.
5. Double-check ACA subsidy and state-tax side effects, then confirm the actual numbers when tax forms arrive so you can calibrate next year's harvest.

A quick sizing rule for December: take the ceiling for your filing status, subtract your projected taxable income (wages and interest minus your standard or itemized deduction), and the remainder is this year's harvest budget. A single filer with $30,000 of taxable income has roughly $18,000 of 0% headroom; a couple with $50,000 has nearly $47,000. Over a decade of early retirement, annual harvesting at that scale can quietly reset the basis on hundreds of thousands of dollars — an estimated $20,000–$60,000 of future tax simply deleted, fifteen minutes a year.

And remember the thresholds are indexed — each January, look up the new 0% ceiling for your filing status before penciling in the year's plan, since a few thousand dollars of drift can change the December math meaningfully.

The bottom line

Tax-gain harvesting is the rare strategy that is simple, legal, riskless to your allocation, and completely ignored by most investors — because it only shines in low-income years, and nobody markets to people having one. If your income dips below the 0%-gains threshold for any reason, don't let December pass without checking your headroom. Erasing future tax bills fifteen cents on the dollar, for the price of two trades, is as close to a gift as the tax code offers.