What is tax-gain harvesting at the 0% capital-gains bracket and how does it help FIRE'd retirees?

Tax-gain harvesting means deliberately selling appreciated investments while your taxable income is low enough that long-term capital gains are taxed at 0%, then immediately rebuying to reset your cost basis higher. For 2025, married-filing-jointly couples pay 0% on long-term gains until taxable income (including those gains) crosses roughly the top of the 12%-equivalent threshold, around $96,700 of taxable income. Early retirees with little earned income can harvest gains for free, locking in a higher basis so future sales trigger less tax. Unlike tax-loss harvesting, there's no wash-sale rule on gains, so you can rebuy the same fund instantly. Balance it against ACA subsidies, since realized gains raise your MAGI. Done annually, this quietly washes out years of unrealized gains at zero cost. Estimate your room at wealthserene.com/tools/capital-gains.