This article is educational and is not legal or tax advice; confirm how these rules apply to your return, entity, basis, passive-activity limits, and filing position with your tax advisor before you file.
If you own a rental or commercial property, filed a Form 4868 extension, and have not yet filed your 2025 Form 1040, a cost segregation study is one of the few property-level depreciation decisions you can still evaluate before filing the extended return. Cost segregation matters on this return because it can move parts of a building from long-life real property into shorter-life personal property or land improvements, which can increase 2025 depreciation when the property was placed in service in 2025 and the deduction is usable under §469.
A cost segregation study does not create a new deduction over the life of the building; cost segregation accelerates depreciation that would otherwise be spread over the 27.5-year residential rental or 39-year nonresidential real property periods under §168(c). The question for you is narrow: will a cost segregation study completed before the return that uses it is filed produce a 2025 benefit that survives passive-loss limits, bonus-depreciation rules, and your likely holding period?
A cost segregation decision before filing is not about whether depreciation exists; it is about whether the right parts of the property are classified into the right recovery periods on the return you are about to file.
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Can you still add a cost segregation study by October 15, 2026 if you filed a Form 4868 extension and have not yet filed your 2025 return?
Under the Form 4868 extension rules, if you filed a Form 4868 extension and have not yet filed your 2025 individual return, October 15, 2026 is the extended due date for that Form 1040. A cost segregation study must be complete before the return that uses the study is filed, so an owner who filed a Form 4868 extension and has not yet filed the 2025 return should decide before filing whether the study belongs on that return.
If you filed a Form 4868 extension and have not yet filed your 2025 Form 1040, October 15, 2026 does not extend the time to pay 2025 tax under Form 4868 rules, but it can give you time to finalize depreciation classifications before the extended return is submitted. If you file the 2025 return without a cost segregation study, you are not out of options for every property, but the route may change from current-return reporting to a later correction method such as Form 3115 when the conditions for an accounting method change are met.
If your rental or commercial property is reported directly on your Form 1040, such as on Schedule E, and you filed a Form 4868 extension and have not yet filed your 2025 return, October 15, 2026 is the practical filing gate for using a current-year cost segregation study on that 2025 individual return. If the property is held through a partnership filing Form 1065 or an S corporation filing Form 1120-S, that entity does not get the October 15, 2026 individual deadline even when an individual owner filed a Form 4868 extension and has not yet filed the owner’s 2025 Form 1040, because the extended due date for 2025 partnership and S corporation returns was September 15, 2026 under the entity extension rules.
If the property is held by a calendar-year C corporation that filed Form 7004 and has not yet filed its 2025 return, October 15, 2026 is also the extended date for that calendar-year corporate return under Form 7004 rules. If your property is held in a pass-through entity, confirm the entity’s filed status with your tax advisor before relying on an individual Form 4868 extension, because your personal unfiled return does not reopen a partnership or S corporation return that was already due.
What can a cost segregation study change on your 2025 return?
A cost segregation study can reclassify portions of a building into recovery periods that are shorter than the 27.5-year residential rental or 39-year nonresidential real property periods provided under §168(c). In practical terms, an engineering-based cost segregation study built on the methodology in the IRS Cost Segregation Audit Techniques Guide may identify §1245 personal property and land improvements that are depreciated more rapidly than the §1250 building shell.
For a rental building, a cost segregation study may identify items such as certain floor finishes, specialty electrical systems, appliances, cabinetry, exterior site lighting, paving, fencing, and landscaping when the property facts support those classifications under §1245, §1250, and §168. For a commercial property, cost segregation may identify qualifying tenant improvements, process-related electrical or plumbing, decorative millwork, specialty finishes, signage, parking lot components, and site improvements when the facts and invoices support the allocation.
The study changes the timing of depreciation, not the total depreciable basis, because the same building basis is recovered over time under §168 when the property is held long enough. The benefit is strongest when the accelerated deduction offsets income you can actually use in 2025, and it is weaker when §469 suspends the loss or when a near-term sale triggers §1245 recapture that reduces the timing value.
Before you file, the key documents are the closing or settlement statement, construction costs and invoices or contractor pay applications, the current depreciation schedule, and a land-value source such as an assessor ratio or appraisal. If those records are incomplete, a cost segregation study may still be possible, but the result depends on whether enough cost detail exists to support reasonable engineering-based allocations.
How does 2025 bonus depreciation affect property placed in service in 2025?
Under §168(k), as amended by OBBBA (2025), bonus depreciation is 100%, permanently, for qualified property acquired after January 19, 2025. IRS Notice 2026-11 ties the word acquired to the written binding contract date rather than the closing date, so a property closed after January 19, 2025 may still fall under the older rule when the written binding contract was signed on or before January 19, 2025.
If qualified property was acquired after January 19, 2025 under IRS Notice 2026-11 and placed in service in 2025, the 5-year, 7-year, and 15-year property identified by a cost segregation study may qualify for 100% bonus depreciation under §168(k). If property was acquired on or before January 19, 2025 and placed in service in 2025, the 2025 bonus rate remains 40% under the TCJA phase-down as applied through §168(k).
Bonus depreciation under §168(k) applies only to property with a recovery period of 20 years or less, so it can apply to qualifying 5-year, 7-year, and 15-year components from a cost segregation study but not to the 27.5-year residential rental building shell or 39-year nonresidential building shell under §168(c). Land is not depreciable under §167 and §168, so a cost segregation study should separate land from depreciable improvements before any bonus depreciation calculation is made.
The acquisition-date rule is especially important for owners who signed purchase contracts before January 19, 2025 but closed later in 2025, because IRS Notice 2026-11 looks to the written binding contract date when determining whether the OBBBA 100% bonus rule applies. If your contract date and placed-in-service date are not clear from the closing file, your tax advisor should review the contract, amendments, and possession facts before the 2025 return is filed.
Will passive-loss rules let you use the depreciation this year?
A cost segregation study helps your 2025 cash tax result only when the accelerated depreciation can be used on the return under the applicable loss rules. Under §469, rental losses are passive unless an exception applies, so a large depreciation deduction from cost segregation may be suspended when you do not have passive income or another rule that makes the loss usable.
Under §469(i), the active-participation rental real estate allowance can permit up to $25,000 of rental loss, and that allowance phases out between $100,000 and $150,000 of modified adjusted gross income. If your modified adjusted gross income is above the §469(i) phaseout range, the active-participation allowance may not let you use the additional depreciation in 2025.
Under §469(c)(7), real estate professional status requires more than 750 hours and more than half of personal services in real property trades or businesses, and the rental losses are nonpassive only when the taxpayer also materially participates in the relevant rental activity. If you meet those §469(c)(7) and material-participation conditions, cost segregation may produce a more immediate 2025 benefit than it would for a passive investor with no passive income.
For short-term rentals, Treas. Reg. §1.469-1T(e)(3)(ii)(A) provides that an activity with an average customer stay of 7 days or less is not treated as a rental activity, and the losses are nonpassive only when material participation is satisfied. If the short-term rental fails material participation, cost segregation may still increase depreciation, but §469 can suspend the loss rather than reduce current tax.
Suspended passive losses carry forward under §469(b), and suspended passive losses are generally released on a fully taxable disposition under §469(g). If your 2025 cost segregation deduction will be suspended, the study may still be useful for long-term planning, but it may not solve a current-year tax payment problem.
When is a cost segregation study usually worth considering before you file?
ClickDrag Finance screens for cost segregation on three conditions: the owner can use the added deduction this year under §469 or another applicable rule, the expected hold period is long enough that §1245 recapture on sale does not erase the timing benefit, and the depreciable building basis excluding land is large enough to clear the study fee — the widely quoted $500K floor was calculated against $40,000–$70,000 engineering studies, so it moves down as the fee does, while the usability and hold-period conditions hold at any price. That screening benchmark is not a tax rule, so a smaller property can still fit when the building has unusually high short-life components, and a larger property can fail when the deductions are suspended or the owner plans to sell quickly.
The hold period matters because cost segregation often converts part of the building into §1245 property, and §1245 recapture can convert prior depreciation into ordinary income on sale when the asset is sold at a gain. If you expect to sell soon, the value of accelerated depreciation depends on your tax rates, sale timing, passive-loss position, and whether the buyer’s price allocates value to assets that created accelerated deductions.
The placed-in-service date also matters because depreciation begins when the property is ready and available for its intended use under §167 and §168. If you bought a building in 2025 but did not place it in service until 2026, the study may still be useful, but the depreciation generally belongs on the 2026 return rather than the 2025 return.
If you want a fast first screen before filing, start with ClickDrag Finance’s cost segregation qualifier so you can test basis, property type, placed-in-service date, and deduction usability before ordering a study. If you want to compare study providers and methods, read our guide to the best cost segregation companies before choosing who prepares the analysis.
What should you do before filing your extended 2025 return?
First, confirm who owns the property for tax purposes, because a Form 4868 extension helps an individual Form 1040 filer only when the individual return has not yet been filed. If the asset is inside a partnership or S corporation, the entity return deadline and depreciation reporting may already control the result, even when your individual return remains unfiled.
Second, confirm whether the property was placed in service in 2025, because a cost segregation study affects the 2025 return only when the building or improvement was ready and available for use in 2025 under §167 and §168. Third, confirm whether the written binding contract date was after January 19, 2025 under IRS Notice 2026-11, because that date controls whether §168(k) bonus depreciation is 100% or remains subject to the 40% 2025 TCJA phase-down.
Fourth, review whether §469 will let you use the deduction, because a cost segregation study that produces suspended passive losses may not reduce 2025 tax. Fifth, gather the settlement statement, invoices or pay applications, depreciation schedule, and land-value support so the study can allocate costs between nondepreciable land, the §1250 building shell, 15-year §1250 land improvements, and §1245 personal property.
If you filed a Form 4868 extension and have not yet filed your 2025 Form 1040, October 15, 2026 is close enough that the right next step is not guessing; the right next step is screening whether cost segregation fits the return you are about to file. You can begin that screen here: check whether your property is a fit before you file.
What if you already filed without cost segregation or placed the property in service in an earlier year?
If you already filed the 2025 return without a cost segregation study, the study cannot be inserted into that filed return as though it had been completed before filing, but later correction routes may be available depending on how many returns have already depreciated the property. If property was placed in service in an earlier year and was depreciated on two or more filed returns without a study, Rev. Proc. 2015-13 automatic change procedures generally allow Form 3115 to be filed with a current-year return and allow missed depreciation to be taken as a §481(a) adjustment without amended returns.
If only one filed return has included the property, the correction is generally made through an amended return rather than Form 3115, and you should confirm the route with your tax advisor before making the change. A Form 3115 catch-up can be powerful when the conditions apply, but it is a different project from claiming cost segregation on an unfiled 2025 extended return.
If your property is in an Opportunity Zone structure, depreciation, basis, and exit rules can interact with cost segregation in ways that need additional review, so see our Opportunity Zone cost segregation guide before filing. If your property is not in an Opportunity Zone, the same core question still controls: does accelerated depreciation improve your return after §168(k), §469, §1245, and your filing status are considered?
Frequently Asked Questions
Can I use cost segregation on my 2025 return if I filed a Form 4868 extension?
Yes, you can use cost segregation on your 2025 Form 1040 if the study is complete before you file, the property was placed in service in 2025 or otherwise qualifies for the method used, and your Form 4868-extended return has not yet been filed. The study changes depreciation classifications on the return, but your tax advisor should confirm ownership, basis, and §469 loss usability before filing.
Does October 15, 2026 apply to my rental property if I filed a Form 4868 extension and have not yet filed?
Yes, October 15, 2026 applies to your 2025 individual Form 1040 if you filed a Form 4868 extension and have not yet filed that return. The same sentence does not apply to a partnership Form 1065 or S corporation Form 1120-S entity return, because those 2025 entity returns on extension were due September 15, 2026 under the entity extension rules.
Will bonus depreciation apply to the assets found in a cost segregation study?
Yes, bonus depreciation can apply to qualifying short-life assets found in a cost segregation study when §168(k) applies, the property has a recovery period of 20 years or less, and the acquisition and placed-in-service conditions are met. Under §168(k), as amended by OBBBA (2025), qualified property acquired after January 19, 2025 can receive 100% bonus depreciation, while property acquired on or before January 19, 2025 and placed in service in 2025 remains at 40% under the TCJA phase-down.
Can depreciation from cost segregation be wasted by passive-loss limits?
Yes, depreciation from cost segregation can be suspended when §469 treats your rental loss as passive and you lack passive income or another applicable exception. Suspended losses carry forward under §469(b) and may be released on a fully taxable disposition under §469(g), but that does not create the same 2025 cash-tax benefit as a currently usable deduction.
Can Form 3115 fix missed depreciation if I do not finish a study before filing?
Yes, Form 3115 can fix missed depreciation when the property has been depreciated on two or more filed returns and Rev. Proc. 2015-13 automatic change procedures apply. If only one return has been filed with the property on it, the correction is generally an amended return instead, so confirm the correct path with your tax advisor before filing or changing depreciation.