The 30-second answer
Yes, you can do cost segregation retroactively on a property you have owned for years, and it is often the best version of the strategy. A Form 3115 change in accounting method lets you claim every year of missed accelerated depreciation as a single §481(a) catch-up deduction on this year's return, with no need to amend prior years. A property bought in 2019 to 2024 without a study can generate a large one-time deduction now.
How retroactive cost segregation works
When you do a study years after purchase, you are not just changing depreciation going forward, you are correcting the accounting method for the whole life of the asset. The mechanism is Form 3115 (Application for Change in Accounting Method):
- The study reclassifies the basis as if it had been done in the year you placed the property in service.
- Form 3115 computes the difference between the depreciation you took (slow, straight-line) and what you could have taken (accelerated, with bonus) across every year you owned it.
- That cumulative difference is the §481(a) catch-up, a single deduction you claim in full on the current year's return.
- No amended returns. The catch-up replaces the need to refile prior years.
For the filing mechanics, see our Form 3115 guide. The catch-up deduction is often larger than a fresh first-year study, because it stacks multiple years of missed depreciation into one.
Who should look at this
- You bought a rental, STR, or commercial property in 2024 or earlier and never had a cost segregation study.
- You have been depreciating it straight-line over 27.5 or 39 years.
- You still own it and plan to hold a few more years.
Properties acquired in 2019 to 2024 are the sweet spot: enough years of missed depreciation to make the catch-up substantial, with the property still in your portfolio. Estimate your number with the calculator.
A note on bonus depreciation in the lookback
The catch-up applies the bonus depreciation rate that was in effect in the year the property was placed in service (for example, 100% for 2019 to 2022, then the phase-down years). Your study and Form 3115 use the correct historical rate per component, which your CPA relies on when filing.
Related: cost segregation after purchase · §481(a) catch-up calculator.