Look-back studies & Form 3115
You don't have to have bought the building this year. A look-back study recovers the accelerated depreciation you missed on a prior-year acquisition — claimed in one catch-up adjustment, without amending old returns.
1How a look-back study works
A standard cost-segregation study reclassifies components in the year a property is placed in service. A look-back study does the same analysis on a property placed in service in an earlier year, then files IRS Form 3115 (Change in Accounting Method) to correct the depreciation method going forward and to claim the difference for all prior years at once.
2The §481(a) catch-up adjustment
The mechanism that makes it work is the §481(a) adjustment: the cumulative difference between the depreciation actually taken and what the cost-segregated method would have allowed is claimed as a single deduction on the current-year return. Prior returns are not amended. A negative §481(a) adjustment (more depreciation) is generally taken entirely in the year of change.
3What buyers get wrong
- Thinking the window has closed. A look-back study is a method change, not a missed election — it's available as long as you still own and depreciate the property.
- Assuming you must amend. You don't; the §481(a) adjustment replaces amended returns.
- Ignoring recapture on a near-term sale. Accelerated depreciation is recaptured on sale (§1245 as ordinary income), so a short remaining hold can erode the timing benefit — a CPA question on your facts.
- Under-weighting documentation. A method-change filing should rest on a well-documented, defensible study; weight methodology and audit-support terms when choosing a provider.
4Frequently asked
Can I do a cost segregation study on a property I bought years ago?
Yes. A look-back (catch-up) study analyzes a property placed in service in a prior year and files a Form 3115 to claim the depreciation that wasn't accelerated at the time — without amending prior returns.
Do I have to amend prior returns?
No. That's the point of the Form 3115 / §481(a) mechanism: the missed depreciation is claimed as a single catch-up adjustment on the current-year return, so prior years are left alone.
How far back can a look-back study go?
Generally to the property's placed-in-service date, provided it's still owned and depreciating. The §481(a) adjustment captures the cumulative difference between the depreciation taken and what a cost-segregated method would have allowed.
Is a look-back study more likely to be scrutinized?
A change in accounting method is a formal filing, so the study needs to be well-documented and defensible. That's a reason to weight methodology and audit-support terms when choosing a provider — see how we compare.
Related: the glossary (Form 3115 / §481(a)), how we compare providers, and the property-type guides. This is general information, not tax advice — confirm treatment with your CPA.