Why It Matters
Your adjusted basis is the number that decides your tax bill at sale. The formula is simple: Original Basis + Capital Improvements - Depreciation Taken = Adjusted Basis. Then: Sale Price - Selling Costs - Adjusted Basis = Taxable Gain. Every $10,000 roof replacement or kitchen renovation increases your basis, which reduces your gain. Every year of MACRS depreciation decreases it, which increases your gain. Here's the trap most investors miss: the IRS uses the "allowed or allowable" rule. If you could have claimed $50,000 in depreciation over 10 years but never filed for it, the IRS still reduces your basis by $50,000 when you sell. You lose the deductions and get taxed as if you took them. That's why you should always claim your depreciation — you're paying the tax consequences either way.
At a Glance
- What it is: Any change to your property's tax basis after purchase — increases from improvements, decreases from depreciation and casualty losses
- Formula: Adjusted Basis = Original Basis + Capital Improvements - Depreciation Taken
- What increases basis: Capital improvements (roof, HVAC, renovation), closing costs capitalized at purchase
- What decreases basis: Annual depreciation, casualty loss deductions, easements granted, insurance reimbursements
- Why it matters: Your adjusted basis determines your taxable gain at sale — higher basis means less tax
- The trap: The IRS "allowed or allowable" rule reduces your basis by depreciation you COULD have claimed, even if you didn't
Adjusted Basis = Original Basis + Capital Improvements - Depreciation Taken
How It Works
Building your original basis. Your starting basis isn't just the purchase price. Add your share of closing costs that get capitalized — title insurance, attorney fees, recording fees, transfer taxes, and survey costs. Buy a property for $250,000 with $6,000 in capitalized closing costs and your original basis is $256,000. The land portion ($50,000 in this case) is separated out because land doesn't depreciate — only the building ($206,000) goes on a MACRS depreciation schedule.
Increases: capital improvements. Every dollar you spend on a capital improvement adds to your basis. New roof for $12,000? Basis goes up $12,000. HVAC replacement for $8,000? Up another $8,000. Kitchen renovation for $15,000? Up $15,000. Over 10 years, these rehab costs can add $30,000-$50,000 to your basis — and that's $30,000-$50,000 less in taxable gain when you sell. The key distinction: repairs (patching a leak, fixing a faucet) are expensed in the year you pay. Improvements (replacing the roof, installing new systems) are capitalized to your basis. Keep every receipt.
Decreases: depreciation. Each year you claim depreciation, your basis drops. A $206,000 building depreciated straight-line over 27.5 years loses $7,491/year in basis. After 10 years, that's $74,909 removed. Bonus depreciation accelerates this — if you take $30,000 in bonus depreciation on appliances and short-lived components in year one, your basis drops $30,000 immediately. Depreciation is powerful for sheltering income, but it lowers your basis, which means more taxable gain at sale. That deferred tax comes due eventually through depreciation recapture at 25% federal.
The "allowed or allowable" rule. This is the single most important thing to understand. IRC Section 1016(a)(2) says your basis is reduced by depreciation "allowed or allowable" — whichever is greater. If you owned a rental for 10 years and never claimed a dime of depreciation, the IRS still reduces your basis by the full $74,909 you could have claimed. You get zero deductions during ownership AND a larger taxable gain at sale. There's no scenario where skipping depreciation saves you money. Always claim it.
Real-World Example
Marcus buys a duplex in 2014 for $250,000. The building portion is $200,000 and land is $50,000. His capitalized closing costs add $6,000 to the building.
Over 10 years, he makes three major improvements: a new roof ($12,000), an HVAC system ($8,000), and a kitchen renovation in one unit ($15,000). Total capital improvements: $35,000.
His annual depreciation on the building: $206,000 / 27.5 = $7,491/year. Over 10 years: $74,909. The improvements depreciate too, but on different schedules — the HVAC components are 5-year property, the roof is 27.5-year. His CPA tracks it all.
In 2024, he sells for $400,000. Selling costs (agent commission, closing): $24,000.
Adjusted basis: $256,000 (original) + $35,000 (improvements) - $74,909 (depreciation) = $216,091.
Taxable gain: $400,000 - $24,000 - $216,091 = $159,909.
The $74,909 in depreciation is recaptured at 25% ($18,727). The remaining $85,000 in gain is taxed at long-term capital gains rates (15-20%). Without those $35,000 in documented improvements, his gain would've been $194,909 — an extra $35,000 taxed at 15-20%.
Every improvement receipt saved him real money.
Pros & Cons
- Every capital improvement increases your basis, directly reducing taxable gain at sale
- Depreciation creates annual tax deductions that shelter rental income from NOI
- Proper basis tracking makes gain calculation straightforward and audit-proof
- Understanding basis adjustments helps you time sales and plan 1031 exchanges strategically
- Forces disciplined record-keeping that protects you in IRS audits
- Depreciation reduces your basis every year, increasing your eventual taxable gain
- Depreciation recapture is taxed at 25% federal — higher than long-term capital gains rates
- The "allowed or allowable" rule penalizes you even if you never claimed depreciation
- Tracking basis across decades of ownership requires meticulous records that many investors neglect
- Land allocation (non-depreciable) is often disputed by the IRS if your split is aggressive
Watch Out
Never skip claiming depreciation — the IRS charges you for it anyway. The "allowed or allowable" rule means your basis drops by the depreciation you could have taken, whether you filed for it or not. If you've missed years of depreciation on a rental property, file Form 3115 (Change in Accounting Method) to catch up. You'll get the accumulated deductions in the current year and your future basis calculation will be correct. A CPA can handle this.
Document every capital improvement like your tax bill depends on it — because it does. Keep invoices, contractor agreements, before/after photos, and a running log of improvements with dates and amounts. The IRS can challenge your basis 3 years after you file the return for the year you sell. If you can't prove the $35,000 in improvements, your basis drops and your tax bill rises. A simple spreadsheet updated after every project saves thousands at sale.
Ask an Investor
The Takeaway
Cost basis adjustment is the mechanism that determines your tax bill when you sell a rental property. Capital improvements push your basis up — reducing gain. Depreciation pulls it down — increasing gain. The MACRS system governs the depreciation side, and every rehab cost that qualifies as a capital improvement works in your favor. The critical rule: always claim your depreciation, because the IRS reduces your basis whether you take the deduction or not. Keep records of every improvement, track your basis annually, and you'll never face a surprise tax bill at closing.