Capital gains when you sell a California home

Under Section 121 of the Internal Revenue Code, you can exclude up to $250,000 of gain from federal tax when you sell your main home, or up to $500,000 if you're married filing jointly.

Two tests gate it. The ownership test: you owned the home at least 24 months of the five years before the sale. The use test: you lived in it as your principal residence at least 24 months of that same five-year window. The months need not be consecutive. You also can't have used the exclusion on another sale within the prior two years.

The exclusion amounts were set in 1997 and have never been indexed to inflation. Bay Area home values since 1997 have not held still.

Work an example. A couple bought in Palo Alto in 1998 for $600,000 and sells today near the $3.47 million median. Their gain before adjustments is roughly $2.87 million. The $500,000 exclusion covers a bit over 17% of it. The remainder is taxable — federal capital gains, the net investment income tax where applicable, and California, which taxes capital gains as ordinary income.

This is not an edge case in Silicon Valley. It is the ordinary situation for anyone who bought before roughly 2010 and stayed. Long tenure and Prop 13 keep people in place, and the same tenure that made the house affordable to hold makes the eventual gain enormous.

Your basis is not just the purchase price. Capital improvements — a new roof, an addition, a kitchen remodel, a permitted ADU — add to it. Routine repairs and maintenance do not. Selling costs, including commission, come off the amount realized.

This is the concrete reason to keep improvement records for as long as you own the home. Twenty years of receipts for permitted work can shift the taxable gain by six figures, and reconstructing them at closing is nearly impossible. If you have a remodel folder in a drawer somewhere, that folder is a financial asset.

There's a quiet corollary about commission: because selling costs reduce the amount realized, the effective after-tax cost of a large commission is somewhat lower than the sticker figure. It's a real effect, and it's a smaller one than most people assume — it reduces the sting, it doesn't erase it.

This guide is an orientation, not tax advice, and the details matter enormously at these numbers. Partial exclusions exist for sales driven by work, health, or unforeseen circumstances. Rules differ if the home was ever a rental, if you inherited it, or if you're a surviving spouse. Nonqualifying-use periods after 2008 reduce the exclusion pro rata.

The IRS lays the framework out in Publication 523 and Topic 701. But on a Bay Area sale the tax question is frequently larger than the commission question, and it deserves a professional who can see your whole return. Have that conversation before you list, not after — some of the useful moves have timing requirements.