The 30-second answer
Yes. You can do a cost segregation study at any point while you own the property, not just in the year you buy it. Doing it in the purchase year is cleanest, but if you bought one, three, or five years ago and never did a study, a Form 3115 lookback lets you catch up all the missed depreciation in a single current-year deduction. There is no deadline that closes the door while you still own the asset.
When is the best time to do it?
- The year you place the property in service is the simplest: the study feeds straight into that year's return, no method change needed.
- Any later year while you own it works too, via a Form 3115 change in accounting method that captures the missed depreciation as a retroactive §481(a) catch-up.
- Before a year where you especially need the deduction (a high-income year, a year with a large passive gain to offset) can be the smartest timing, since the catch-up lands in that year.
How late is too late?
As long as you still own the property, it is not too late. The lookback captures depreciation back to the placed-in-service date. The only thing that closes the window is selling, once you dispose of the property, you lose the chance to do a study on it (though there are related strategies at disposition your CPA can discuss). If you are holding a property you bought in 2024 or earlier without a study, you are leaving deductions on the table.
Just bought? Do this
If you closed recently, order the study in time to file the current year's return so the deduction lands in Year 1. Cost Seg Smart studies are delivered in 1–2 business days for simple residential, so there is no scheduling lag, even close to a filing deadline. Estimate your Year-1 number with the calculator, or see a real report example.
Related: retroactive cost segregation · §481(a) catch-up calculator · Form 3115 walkthrough.