What home improvements add to your cost basis?

When you sell your home, you're taxed on your gain — roughly the sale price minus what the home “cost” you. That cost figure is your cost basis, and it isn't just the purchase price. Most of the capital improvements you make over the years get added to it, which shrinks your taxable gain dollar-for-dollar. The catch: you can only count improvements you can prove.

Basis, in one line

Your adjusted cost basis is what you paid for the home plus qualifying capital improvements, minus a few things like energy credits and any depreciation you took. A higher basis means a smaller gain — and gain above the $250,000 / $500,000 exclusion is where the tax actually bites.

Improvements that increase basis

IRS Publication 523 describes an improvement as work that adds to your home's value, prolongs its useful life, or adapts it to new uses. Its examples include:

• Additions — a bedroom, bathroom, deck, garage, porch, or patio.
• Lawn & grounds — landscaping, a driveway, walkway, fence, retaining wall, or swimming pool.
• Systems — heating, central A/C, a furnace, ductwork, wiring, a security system, or a lawn sprinkler system.
• Exterior — a new roof, new siding, storm windows or doors.
• Insulation — in the attic, walls, floors, or around pipes and ductwork.
• Plumbing — a septic system, water heater, or water filtration/softening system.
• Interior — a kitchen remodel, new flooring, built-in appliances, wall-to-wall carpeting, or a fireplace.

There is no cap on how much you can add to basis this way — a $200,000 addition counts as fully as a $2,000 water heater, as long as it qualifies and you kept the records.

What doesn't count

Routine repairs and maintenancethat keep the home in good condition but don't add value or prolong its life — painting, fixing a leak, patching a crack, replacing a broken handle — are not added to basis. The line between an improvement and a repair trips a lot of people up; we cover it in capital improvements vs. repairs.

Two more things reduce basis rather than add to it: improvements you later remove or replace (if you rip out carpet and put in hardwood, only the hardwood counts), and energy credits or subsidies you received on things like solar.

Why documentation is the whole game

Here's the part people miss: your improvements add to basis only if you can substantiate them. At sale, your adjusted basis is just a number on your return — the invoices aren't attached. But if the IRS ever audits, those records are what stand behind the number. A pile of improvements you can't prove is, to the IRS, no improvements at all.

That's the case for logging each project as you go — while the invoice is still in your inbox — instead of reconstructing decades of work under audit pressure.