Long-term capital gains are taxed at 0%, 15%, or 20%, with brackets stacked on top of ordinary income. The 0% bracket reaches up to roughly $49,000 of taxable income for singles in 2026 and $98,000 for married couples filing jointly (indexed annually; verify the current year’s figure before sizing the harvest). Within that zero-bracket headroom, any LTCG you realize costs zero federal tax. The gain becomes new basis; sell and immediately rebuy and you have stepped up your basis at no federal cost.
Read those thresholds carefully—they are taxable income limits, not gross income limits. The standard deduction ($16,100 single / $32,200 MFJ in 2026 under the OBBBA-bumped figures) stacks first against ordinary income, and what is left of the 0% headroom is yours to harvest. A retiree with zero ordinary income, taking the standard deduction, can realize roughly $65,100 single or $130,200 MFJ of gross long-term capital gains before owing a dollar of federal capital-gains tax. The early-retirement years between leaving W-2 income and starting Social Security are precisely when that condition holds; in a clean conversion-window year you can choose between filling the bracket with a Roth conversion (ordinary income) or with a gain harvest (LTCG), but not both.
In the early retirement and bridge years, low ordinary income leaves significant room under that ceiling. Used annually, the harvest functions as a reverse loss-harvest: realize gains while they cost nothing, raise your basis, and shrink the future tax liability of every subsequent sale. Coordination with the conversion window matters: a Roth conversion fills ordinary-income bracket space and pushes LTCG out of the 0% zone. You cannot harvest gains and convert into the same brackets in the same year; choose which lever each cheap year serves.
The IRMAA caveat Realized LTCG counts dollar-for-dollar in IRMAA MAGI even when it costs zero income tax. A retiree who harvests $80,000 of 0%-bracket gains and then discovers two years later that the harvest crossed an IRMAA tier has saved zero in income tax and paid several thousand in Medicare premiums. The harvest belongs inside the same MAGI ceiling that governs conversions. The 0% bracket is free of income tax, not free of consequence.
The state caveat A handful of states do not match the federal preferential LTCG treatment—California taxes LTCG as ordinary income at the same brackets as wages, topping at 13.3% (a 12.3% top ordinary bracket plus the 1% Behavioral Health Services Tax on income above $1M). A federal 0% harvest in Santa Clara is still a 12.3%–13.3% state ordinary-income event. Run the harvest where you are domiciled (section “Domicile and the Conversion Year”).
Versus the step-up Inherited assets receive a basis step-up at the decedent’s death under IRC §1014, “Basis of property acquired from a decedent”. For a position with a very large embedded gain held by an elderly owner, the cheapest tax on that gain is zero, and the way to get there is to hold and die. The 0%-bracket harvest is best applied to positions where step-up is many years away, holding periods are not yet long-term, or you want to rebalance out of a concentrated holding without paying for it.