Filing your return does not forfeit the deduction; it just changes which door you use. There are 3 paths to capture bonus depreciation from a cost segregation study after the return has gone in: supersede, amend, or catch up next year on Form 3115.
Path 1: superseding return
If you are on extension, a corrected return filed before the extended due date is a superseding return and is treated as your original. This is the cleanest fix: drop the study's classes and bonus depreciation under IRC section 168(k) straight into the return as if the first filing never happened.
Path 2: amended return
Once the deadline has passed, you can amend within the refund window of IRC section 6511, generally 3 years from filing. Amending works for depreciation only while the treatment is not yet an established method, meaning you have filed just one return since the property was placed in service (Reg. 1.446-1(e)(2)(ii)(d)). Buy in 2025, file the 2025 return, amend the 2025 return: allowed.
Path 3: Form 3115 with next year's return
If 2 or more returns have already used the wrong lives, the fix is an automatic accounting method change under Rev. Proc. 2015-13. Form 3115 attaches to the next return, and the entire shortfall, including bonus at the rate your original acquisition and placed-in-service dates support, arrives as a negative section 481(a) deduction in that year. You lose nothing except timing.
Worked example: a 2025 short-term rental
An investor closed on a $950,000 short-term rental in May 2025, allocated $190,000 to land, and filed the 2025 return in February 2026 with the $760,000 building on a 39-year schedule, correct for an STR whose average stay runs under 30 days per the transient-use rule in IRS Pub 946. A study then reclassifies 30%, or $228,000, into 5, 7, and 15 year property. Because the property was acquired after January 19, 2025, the permanent 100% bonus rate under IRC section 168(k) as amended by OBBBA applies, so the study supports a $228,000 first-year deduction. No extension was filed, so superseding is off the table; with only one return filed, the investor amends 2025 and claims the full amount. Whether the loss offsets W-2 income depends on the separate 7-day average stay and material participation tests of Reg. 1.469-1T(e)(3).
Caveats
Property acquired on or before January 19, 2025 keeps the phase-down rates (80% for 2023, 60% for 2024, 40% for 2025 placements), so any catch-up is computed at those rates, not 100%. An amended return reopens that year to examination generally; a Form 3115 does not reopen anything. And bonus cannot be claimed at all if you affirmatively elected out of it for that property class in the original year.
Amadae screens the property, models the first-year deduction in its free Tax Strategy Projector, and prepares whichever filing the timeline requires: superseding, amended, or Form 3115 with the section 481(a) catch-up math.