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Audit support includedFlat price for every study3 to 5 business days Filing Form 3115 after a cost segregation study on a residential rental lets you catch up depreciation you missed in prior years, all inside the current-year tax return, with no need to amend anything. The form applies when the study happens after the property's placed-in-service year; same-year studies use Form 4562 instead and never touch Form 3115.
- Form 3115 cost segregation residential rental filings catch up missed depreciation without amending prior returns.
- File it when the study happens after year one; same-year studies use Form 4562 instead.
- The Section 481(a) adjustment reports the full catch-up as one deduction in the current tax year.
- Automatic consent under Rev. Proc. 2015-13 covers most residential cost segregation catch-up filings.
- Bonus depreciation sits at 100% for property acquired and placed in service after January 19, 2025 under the OBBBA.
Why This Matters
A cost segregation study reclassifies parts of a residential rental (flooring, appliances, land improvements) into 5, 7, and 15-year property instead of the standard 27.5-year schedule. If that study happens in the year you buy or convert the property, your CPA reports the reclassified depreciation straight on Form 4562 and moves on.
The problem shows up when the study happens later. Say you bought a short-term rental in 2023, filed two years of returns using straight-line depreciation, then ordered a study in 2026. You can't just plug the new numbers into this year's return and call it done, because the prior two years already claimed the wrong amount. That's what Form 3115 after a residential cost segregation study exists to fix.
When Does a Residential Rental Need Form 3115 After Cost Segregation?
The test is simple: has the property been in service for at least one full tax year before the study happens?
- Property placed in service and studied in the same tax year – no Form 3115. Depreciation goes on Form 4562 as originally filed.
- Property placed in service in a prior year, studied later – Form 3115 is required to catch up the difference between what was claimed and what should have been claimed.
- Prior returns already filed using straight-line depreciation – this is the trigger event. Once at least one return has been filed with the old method, you can't simply amend your way out of it for a permissible-to-permissible method change; the IRS routes this through the automatic accounting method change procedure instead.
- CPA files Form 3115 with the current-year return – attached to the return for the year the study is completed, not the year the property was purchased.
Cost Segregation in the Placed-in-Service Year: No Form 3115 Needed
When the study lands in the same tax year the rental goes into service, there's nothing to catch up. The reclassified asset classes flow directly onto Form 4562 as part of the original depreciation schedule. This is the cleanest scenario and the one most owners aim for by ordering a study before their first return is filed.
Cost Segregation After Year One: Form 3115 Required
Once a return has already been filed using the default 27.5-year residential schedule, a later cost segregation study creates a mismatch between what was claimed and what the engineering-based reclassification says should have been claimed. Form 3115 exists specifically to resolve that mismatch through a single current-year adjustment instead of a stack of amended returns.
Why Form 3115 Requirements Vary
Whether your CPA needs to file Form 3115, and how the catch-up gets calculated, depends on a handful of facts specific to the property and the return history:
- Whether the cost segregation study happens in the same tax year as the placed-in-service date or a later year
- Whether at least one prior return has already been filed using straight-line depreciation
- Which Designated Change Number (DCN) applies to the change (residential rental catch-ups typically fall under DCN 7 for a change to a permissible depreciation method)
- The size of the missed depreciation and whether it interacts with passive activity loss limits for the owner
- Whether the property has changed ownership structure (LLC, trust, or partnership) between the placed-in-service date and the study date
- Timing relative to the return's original or extended filing deadline for the current tax year
Does Form 3115 Require Amending Prior Tax Returns?
No, amending prior returns is exactly what Form 3115 avoids. Instead of refiling every year that used the wrong depreciation method, the entire catch-up amount is reported as a single Section 481(a) adjustment on the current-year return, which is one of the main reasons CPAs prefer it for look-back cost segregation studies.
What Is the Section 481(a) Adjustment on Form 3115?
The Section 481(a) adjustment is the lump-sum figure that represents the total difference between depreciation actually claimed and depreciation that should have been claimed under the corrected method. It gets reported in full in the year of the accounting method change, which for a residential rental typically means one large deduction the same year the cost segregation study is completed. Your CPA calculates this figure directly from the asset classifications in the cost segregation report.
Which Designated Change Number (DCN) Applies to a Missed Depreciation Catch-Up?
DCN 7 covers a change to a permissible method of accounting for depreciation, which is the designation most residential rental owners use when correcting under-depreciation after a cost segregation study. This falls under the automatic consent procedures in Rev. Proc. 2015-13, meaning IRS pre-approval isn't required before filing, though the form still has to be attached to a timely filed return.
A report built for this purpose matters here. Virtual Cost Segregation produces an engineering-based, audit-defensible report with the asset-by-asset detail a CPA needs to compute the 481(a) adjustment correctly, whether the study lands in year one or year five of ownership.
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FAQ
Does every cost segregation study on a residential rental require Form 3115?
No, only studies ordered after the property's placed-in-service tax year require Form 3115. Same-year studies report reclassified depreciation directly on Form 4562 with no catch-up needed.
How far back can Form 3115 catch up missed depreciation on a rental?
Form 3115 can capture the full cumulative difference between what was claimed and what should have been claimed since the placed-in-service date, regardless of how many years have passed. The entire amount reports as one Section 481(a) adjustment in the current tax year.
Do you need IRS approval before filing Form 3115 for a depreciation method change?
No, most residential rental depreciation corrections fall under automatic consent procedures in Rev. Proc. 2015-13. The form still must be attached to a timely filed return, but a separate approval request isn't required.
What happens if a CPA skips Form 3115 after ordering a late cost segregation study?
Skipping it means the reclassified depreciation from the study never gets picked up on the return, and prior years stay stuck on the original straight-line schedule. The catch-up deduction simply goes unclaimed unless corrected through Form 3115 or amended returns.
Is Form 3115 the same thing as amending a tax return?
No, Form 3115 is an accounting method change filed with the current-year return, not an amendment to a prior-year return. It replaces the need to amend multiple years by consolidating the correction into one current-year adjustment.
Does bonus depreciation change how Form 3115 is calculated in 2026?
Bonus depreciation sits at 100% for residential rental property acquired and placed in service after January 19, 2025 under the OBBBA, which affects how much of the reclassified basis is immediately deductible versus depreciated over 5, 7, or 15 years. The Section 481(a) adjustment on Form 3115 reflects whichever bonus rate applied in the years being caught up.
Who actually files Form 3115, the property owner or the CPA?
The CPA files Form 3115 as part of preparing the owner's tax return; it isn't something a rental owner submits independently. The owner's role is providing the cost segregation report and prior depreciation schedules the CPA needs to calculate the adjustment.
One Last Thing
The automatic consent procedure under Rev. Proc. 2015-13 means a residential rental owner who's owned a property for years, even a decade, can still capture the full missed depreciation in a single current-year deduction. There's no statute-of-limitations cutoff on how far back the Section 481(a) adjustment reaches, which is the detail most owners never hear about until their CPA brings it up.
