This article is educational and is not legal or tax advice; confirm how Form 3115, §481(a), §168(k), §469, §1245, and §1250 apply to your return with your tax advisor before you file.
If you placed a rental, commercial, self-storage, short-term rental, or other investment property in service in an earlier year and never had a cost segregation study done, the question is not just whether you missed depreciation; the question is whether you can still claim that missed depreciation on the return you are about to file. For many owners, cost segregation becomes a look-back project, not a current-year-only project, because Rev. Proc. 2015-13 can allow a Form 3115 method change with a §481(a) catch-up adjustment.
The practical goal of a cost segregation look-back study is to identify building components that were depreciated too slowly as §1250 building property and reclassify qualifying components as shorter-life §1245 personal property and 15-year land improvements. If your return has not been filed yet, the cost segregation study must be complete before the return that uses it is filed, because the Form 3115 and the depreciation schedule need to reflect the study’s allocations.
Bottom line: when Rev. Proc. 2015-13 applies because the property has been depreciated on two or more filed returns under the old method, Form 3115 can move missed depreciation into the current return as a §481(a) adjustment without amended returns.
ClickDrag Finance educational summary of Rev. Proc. 2015-13 and Form 3115 mechanics
Do I use Form 3115 when my property was placed in service in an earlier year?
You generally use Form 3115 for a cost segregation catch-up when the property was placed in service in an earlier year and, under Rev. Proc. 2015-13, the same depreciation method has been used on two or more filed returns. In that situation, the owner is usually changing an accounting method for depreciation, and the missed depreciation is generally taken on the current return as a §481(a) adjustment rather than by amending prior returns.
If only one filed return has included the property under the old depreciation treatment, the correction is generally made by amended return rather than by a Form 3115 automatic method change under the Rev. Proc. 2015-13 framework. Because the line between an amended return correction and a Form 3115 method change depends on the return history, you should confirm the route with your tax advisor before the current return is filed.
For a property owner, the reason this distinction matters is cash flow on the return you are preparing now. A look-back cost segregation study does not create new basis; it accelerates the recovery of the same depreciable basis by moving qualifying assets into shorter recovery classes under §168 and, when available, bonus depreciation under §168(k).
Can I add the cost segregation catch-up to my 2025 return if I am on extension and have not filed?
Yes, if your 2025 return is still unfiled and the study, depreciation schedules, and Form 3115 are ready before that return is filed, a cost segregation catch-up can be included with the current return under Rev. Proc. 2015-13 when the property has been depreciated under the old method on two or more filed returns. If you filed Form 4868, are on extension, and have not yet filed your 2025 Form 1040 return, October 15, 2026 is the extended due date for that individual return under Form 4868.
If the owner is a calendar-year C corporation that filed Form 7004, is on extension, and has not yet filed its 2025 Form 1120 return, October 15, 2026 is the extended due date for that corporate return under Form 7004. If the property is held through a partnership filing Form 1065 or an S corporation filing Form 1120-S, the extended entity return due date was September 15, 2026 under Form 7004, so an entity that has not filed is past its extended due date, and the owner-level 2025 return and any Form 3115 the entity files need your advisor’s attention.
The filing sequence is important because a cost segregation study must be complete before the return that uses the study is filed. If the property was placed in service in 2025, no Form 3115 is needed: the study’s schedule goes on the 2025 return you have not yet filed. If a return is filed without the study, a later correction depends on how many returns have been filed with the old depreciation: with two or more, Form 3115 under Rev. Proc. 2015-13; with only one, generally an amended return.
What does Form 3115 change on this return?
Form 3115 changes the depreciation method for assets that were previously grouped into the long-life building category, and §481(a) measures the cumulative difference between the depreciation already claimed and the depreciation that would have been claimed if the proper method had been used from the placed-in-service date. In a cost segregation look-back, that §481(a) amount is commonly the catch-up deduction reported with the current return when Rev. Proc. 2015-13 allows the automatic accounting method change.
Example in concept: if your apartment building, warehouse, medical office, or retail center was placed in service in an earlier year and the whole depreciable building basis has been depreciated as §1250 real property, a cost segregation study may identify §1245 personal property and land improvements with shorter recovery periods under §168. The Form 3115 then lets the return reflect the cumulative missed depreciation as a §481(a) adjustment when the Rev. Proc. 2015-13 conditions are met.
The study itself should be engineering-based or built on the methodology in the IRS Cost Segregation Audit Techniques Guide. That means the work ties components to construction records, invoices, plans, site information, and cost sources rather than assigning broad percentages without support.
How does bonus depreciation affect the §481(a) catch-up from a cost segregation study?
Bonus depreciation can make the §481(a) adjustment larger when the assets identified by cost segregation are qualified property under §168(k). Under §168(k) as amended by OBBBA (2025), bonus depreciation is 100% for qualified property acquired after January 19, 2025, and IRS Notice 2026-11 ties the acquired date to the written binding contract date rather than the closing date.
If the property was acquired on or before January 19, 2025 and placed in service in 2025, §168(k) keeps that property on the TCJA phase-down schedule with 40% bonus depreciation for 2025. Under §168(k), bonus applies only to property with a recovery period of 20 years or less, which is why the 5-year, 7-year, and 15-year property identified by a cost segregation study matters, and bonus depreciation does not apply to the 27.5-year residential rental shell, the 39-year nonresidential building shell, or land under §168.
For an older placed-in-service property, the bonus rule that applied in the original placed-in-service year is part of the catch-up calculation under §481(a). For a Form 3115 on a 2025 return, that rate is 100% for qualified property acquired after September 27, 2017 and placed in service through 2022, 80% for 2023 and 60% for 2024. Your advisor and study provider should align the acquisition date, placed-in-service date, written binding contract date when relevant under IRS Notice 2026-11, and the original depreciation schedules before the Form 3115 is attached to the current return.
When does catch-up depreciation not help my return?
Catch-up depreciation does not help much if you cannot use the deduction this year because §469 passive-activity rules limit your losses. Under §469, rental losses are generally passive unless an exception applies, and suspended losses carry forward under §469(b) until they can be used or are released on a fully taxable disposition under §469(g).
If you are relying on the active-participation rental real estate allowance, §469(i) allows up to $25,000 of losses and phases that allowance out between $100,000 and $150,000 of modified adjusted gross income. If you are relying on real estate professional status, §469(c)(7) requires more than 750 hours and more than half of personal services in real property trades or businesses, and material participation still matters for the activity.
If your property is a short-term rental, Treas. Reg. §1.469-1T(e)(3)(ii)(A) says an activity with an average customer stay of 7 days or less is not treated as a rental activity, but the loss is nonpassive only when the owner materially participates. In that case, a cost segregation study may be powerful if the owner materially participates and has income that can be offset, but the same study may produce suspended losses if the participation and income facts do not support current use.
Cost segregation is generally worth reviewing when all three conditions are present: the property has roughly $500K or more of depreciable basis excluding land under ClickDrag Finance’s screening rule of thumb, the owner can actually use the accelerated deduction this year under §469 and related limits, and the expected hold period is long enough that §1245 recapture on sale does not erase the timing benefit. Over the life of the building, cost segregation accelerates deductions rather than increasing the total depreciable basis, and §1250 and §1245 character rules still matter when the property is sold.
What records does an engineering-based cost segregation study need before I file?
A look-back cost segregation study usually starts with the closing or settlement statement, construction costs and invoices, contractor pay applications when construction records exist, the current depreciation schedule, and a land-value source such as an assessor ratio or appraisal. These records let the study separate nondepreciable land, long-life §1250 building costs, and shorter-life §1245 components.
For an acquisition, the settlement statement helps reconcile the purchase price, land allocation, closing costs, and depreciable basis. For a build or major renovation, invoices and contractor pay applications help trace costs to electrical, plumbing, flooring, site work, specialty systems, and other components that may have different recovery periods under §168.
The current depreciation schedule is especially important for Form 3115 because the §481(a) calculation compares what was actually claimed with what should have been claimed under the corrected method. Without the existing schedule, the catch-up depreciation estimate may not tie cleanly to the tax return that will report the adjustment.
What should I do before I file the return that will use Form 3115?
First, confirm whether the property has been depreciated under the old method on two or more filed returns, because Rev. Proc. 2015-13 generally points to Form 3115 and a §481(a) catch-up adjustment when that condition is met. Second, confirm whether the deduction will be usable on the current return under §469, because a large depreciation adjustment may be suspended if the activity is passive and no exception applies.
Third, compare the expected benefit against your hold period and exit plan, because §1245 recapture can reduce the value of accelerating deductions if the property is sold soon. Fourth, make sure the study is complete before the return that uses it is filed, because the filed return needs the corrected depreciation schedules and Form 3115 treatment.
If you want to screen your property before filing, start with ClickDrag Finance’s cost segregation qualifier so you can check basis, property type, placed-in-service date, and deduction usability before ordering a study. If you are comparing providers, our guide to the best cost segregation companies lists what to ask each provider about an engineering-based study.
For owners with Opportunity Zone property, the timing and depreciation analysis can have additional basis and exit considerations, so you may also want to read our guide to Opportunity Zone cost segregation. The key is to decide before filing whether the study fits this return, because Form 3115, §481(a), §168(k), §469, §1245, and §1250 all affect how the depreciation actually lands.
Related reading for a 2025 return on extension and not yet filed: claiming cost segregation before the October 15 extended deadline, the January 19, 2025 acquisition cut-off for 100% bonus depreciation, and how a look-back study claims missed depreciation on Form 3115.
Frequently Asked Questions
Can cost segregation catch-up depreciation be claimed without amended returns?
Yes, when Rev. Proc. 2015-13 applies because the property has been depreciated under the old method on two or more filed returns, Form 3115 can report the missed depreciation as a §481(a) adjustment on the current return without amended returns. If only one return has been filed with the property on it, the correction is generally an amended return instead, so confirm the route with your tax advisor.
Does Form 3115 create new depreciation?
No, Form 3115 does not create new depreciable basis because §481(a) measures the difference between depreciation already claimed and depreciation that should have been claimed under the corrected method. Cost segregation changes the timing of deductions by identifying shorter-life §1245 property within the existing depreciable basis.
Can bonus depreciation apply in a look-back cost segregation study?
Yes, bonus depreciation can apply in a look-back cost segregation study when the reclassified assets were qualified property under §168(k) for the relevant placed-in-service year. Under §168(k) as amended by OBBBA (2025), qualified property acquired after January 19, 2025 can receive 100% bonus depreciation, while IRS Notice 2026-11 ties the acquired date to the written binding contract date.
Will depreciation catch-up help if my rental losses are passive?
Not necessarily, because §469 can suspend rental losses when the owner cannot use the losses currently. Suspended losses carry forward under §469(b) and are released on a fully taxable disposition under §469(g), so the current cash-flow value depends on your income, participation, and disposition facts.
What documents should I gather for a cost segregation Form 3115 project?
You should gather the closing or settlement statement, construction invoices or contractor pay applications, the current depreciation schedule, and a land-value source such as an assessor ratio or appraisal. Those documents support the engineering-based allocation, the §168 recovery-class changes, and the §481(a) catch-up calculation reported with Form 3115.
