Converting Your Home to a Rental? The Cost Segregation Basis Trap You Need to Know
The conversion wave is real. But most converting homeowners are walking into a basis calculation they have never encountered.
Matthew Gigantelli
Lead Cost Seg Engineer · ASCSP M009-25
Homeowners locked into 2.8% and 3.2% mortgages from 2020-2021 are not selling — they are converting to rentals. The math is simple: keep the cheap debt while generating rental income. But the tax math on a converted property is fundamentally different from a property purchased as an investment. Three specific traps catch nearly every converting homeowner, and understanding how cost segregation interacts with each is the difference between a tax-efficient conversion and a six-figure mistake.
Trap 1: The Lesser-Of Rule
Under IRC Section 168(i)(5) and Treasury Regulation 1.168(i)-4(b), when you convert personal-use property to business or investment use, your depreciable basis is the lesser of your adjusted cost basis or the property's fair market value at the date of conversion. This is mandatory — you cannot choose the higher number.
Example: Home That Appreciated
You bought for $300,000 in 2019. Current FMV at conversion: $525,000. Your depreciable basis is $300,000 minus land (say $60,000) = $240,000 — not the $420,000 you might expect based on current value. The $225,000 in appreciation is not depreciable.
Example: Home That Depreciated
You bought for $450,000 in 2007. Current FMV at conversion: $380,000. Your depreciable basis is the lesser: $380,000 minus land = approximately $304,000. Here the FMV is lower, so you use it.
Trap 2: Existing Components Do NOT Get Bonus Depreciation
The One Big Beautiful Bill Act restored 100% bonus depreciation — but only for property acquired after January 19, 2025. Your home was acquired years ago. The existing building components do not qualify. However, new improvements made AFTER conversion — new flooring, new HVAC, new landscaping — DO qualify for 100% bonus depreciation if placed in service after 1/19/2025. This creates a strategic planning opportunity: time your renovation improvements to occur after conversion to maximize bonus-eligible deductions.
Trap 3: The Section 121 Exclusion Clock Is Ticking
The $250,000/$500,000 capital gains exclusion under IRC Section 121 requires that you lived in the property for at least 2 of the last 5 years before sale. Every year as a rental erodes your ability to sell tax-free. If you convert in 2026 and do not sell until 2030, you no longer qualify for the exclusion. Plan your timeline before converting.
Why Cost Segregation Still Matters for Conversions
Even without bonus depreciation on existing components, cost segregation reclassifies components to shorter MACRS lives. A 5-year asset depreciated under the 200% declining balance method produces significantly larger deductions in the first 3-5 years compared to 27.5-year straight-line. The study also establishes the component-level basis allocation that becomes the baseline for tracking future improvements — each of which can qualify for bonus depreciation. For a detailed primary residence conversion analysis with OBBBA implications, see Overline's primary residence conversion analysis with OBBBA implications.