Does a Cost Segregation Study Have to Be Done by December 31?

No, a cost segregation study does not have to be finished on the last day of the tax year; for a calendar-year taxpayer, property placed in service by December 31, 2026 can be depreciated on the 2026 return under Treas. Reg. §1.46-3(d)(1)(ii) and Treas. Reg. §1.167(a)-11(e)(1)(i), and the cost segregation study must be complete before the original return that claims the reclassified depreciation is filed (a later study can still be claimed through the catch-up routes below).

The real cost segregation deadline question is whether your rental or commercial property was ready and available for its intended use, whether the cost segregation study can support the depreciation you plan to claim on the 2026 return, and whether a later catch-up route is available if the study is not used on the original return.

For a calendar-year taxpayer, what does property placed in service by December 31 mean?

For a calendar-year taxpayer, property is placed in service by December 31, 2026 only when it is in a condition or state of readiness and availability for its specifically assigned function under Treas. Reg. §1.46-3(d)(1)(ii) and Treas. Reg. §1.167(a)-11(e)(1)(i).

For a rental property, that condition usually means the unit or building is ready and available to rent under Treas. Reg. §1.46-3(d)(1)(ii), not merely that the deed has transferred or that the first tenant has already moved in.

A property bought with tenants in place is usually placed in service at acquisition when the rental operation is already ready and available for its assigned function under Treas. Reg. §1.46-3(d)(1)(ii).

A property bought vacant and needing renovation before it can be rented is usually not placed in service until the rental is ready and available for occupancy under Treas. Reg. §1.46-3(d)(1)(ii).

For a calendar-year taxpayer, property placed in service by December 31, 2026 can start depreciation on the 2026 return under Treas. Reg. §1.46-3(d)(1)(ii), while property placed in service on January 1, 2027 or later is first depreciated on the 2027 return under the same placed-in-service rule.

A fiscal-year taxpayer applies the placed-in-service rule under Treas. Reg. §1.46-3(d)(1)(ii) using the end of that taxpayer’s own tax year, rather than the calendar-year filing pattern.

When does the cost segregation study have to be finished for the 2026 return?

The cost segregation study has to be complete before the 2026 return that claims the reclassified depreciation is filed, because the return needs the study’s allocation of building basis into shorter-life assets and real property categories under §168.

If your building is placed in service in 2026, the cost segregation result belongs on the original 2026 return and no Form 3115 is needed for that current-year placement under section 6.01 of Rev. Proc. 2025-23 and the procedures of Rev. Proc. 2015-13.

That is why the last day of the tax year is not the study-finished line for a new 2026 property; the study is the support for the depreciation position taken on the filed return, not the event that starts depreciation under Treas. Reg. §1.46-3(d)(1)(ii).

A cost segregation study generally uses the closing or settlement statement, construction costs and invoices or the contractor’s pay applications, the current depreciation schedule, and a land-value source such as an assessor ratio or appraisal.

ClickDrag Finance builds each cost segregation review on the methodology in the IRS Cost Segregation Audit Techniques Guide, using property documents to estimate allocations among the building shell, qualified improvement property, land improvements, and tangible personal property.

If you are trying to decide whether to proceed, start with the property facts rather than the calendar; you can check whether the property is a likely fit through the cost segregation qualifier before you ask your tax advisor to model the 2026 return effect.

What changes on my 2026 return if the study is done before I file?

A cost segregation study changes the 2026 return by moving eligible basis from the 27.5-year residential rental building or 39-year nonresidential real property categories into shorter recovery periods when the property facts support that allocation under §168.

Residential rental real property uses a 27.5-year recovery period and nonresidential real property uses a 39-year recovery period under §168(c), while the assets commonly identified in cost segregation include 5-year, 7-year, and 15-year property under §168 and the applicable asset-class guidance.

Bonus depreciation under §168(k), as amended by OBBBA in 2025, is 100% for qualified property acquired after January 19, 2025, when the property otherwise qualifies and is not land or the 27.5-year or 39-year building shell.

IRS Notice 2026-11 ties the acquired date for a written binding contract to the latest of the date the contract was signed, the date it became enforceable under state law, the end of any cancellation period, and the date any contingency was satisfied under Treas. Reg. §1.168(k)-2(b)(5)(ii)(B).

For a written binding contract, the contract must be enforceable under state law and must not limit damages to a specified amount, such as through a liquidated damages clause, under Treas. Reg. §1.168(k)-2(b)(5)(iii).

When a contract is not binding in that sense, the acquired date is generally when the taxpayer has paid or incurred more than 10 percent of the total cost, excluding land and preliminary activities, under Treas. Reg. §1.168(k)-2(b)(5)(iii) and Treas. Reg. §1.168(k)-2(b)(5)(v).

For self-constructed property, including property built for the taxpayer under a written binding contract entered into before construction began, acquisition occurs when physical work of a significant nature begins, and paying or incurring more than 10 percent of the total cost excluding land and preliminary activities is a safe harbor under Treas. Reg. §1.168(k)-2(b)(5)(iv), with the safe harbor stated in Treas. Reg. §1.168(k)-2(b)(5)(iv)(B)(2).

Qualified property acquired on or before January 19, 2025 and placed in service in 2026 generally remains on the TCJA phase-down at 20% bonus depreciation for 2026 under §168(k), except for long-production-period property and certain aircraft described in §168(k)(2)(B) and §168(k)(2)(C).

Used property can qualify for bonus depreciation only when the used-property rules in §168(k)(2)(E)(ii) are satisfied, and a taxpayer may elect out of bonus depreciation for a class of property for a year under §168(k)(7).

Residential rental and nonresidential real property use the mid-month convention under §168(d)(2), under which property placed in service in any part of a month is treated as placed in service at the middle of that month, so a shell placed in service in December of a calendar tax year receives one-half month of first-year regular depreciation.

Other MACRS property identified by a cost segregation study uses the half-year convention unless the mid-quarter convention applies under §168(d)(1) and §168(d)(3).

For a calendar-year taxpayer, property placed in service from October 1 through December 31, 2026 is placed in service in the last three months for the §168(d)(3) mid-quarter test, and fourth-quarter property under the mid-quarter convention receives one and a half months of first-year regular depreciation under §168(d)(3).

The mid-quarter convention applies under §168(d)(3)(A) when the aggregate basis of MACRS property placed in service during the last three months of the tax year is more than 40% of the aggregate basis of all MACRS property placed in service during that year, and §168(d)(3)(B) excludes from that test residential rental property, nonresidential real property, and property placed in service and disposed of in the same year.

Bonus depreciation under §168(k) is not reduced by the §168(d) convention, so the mid-quarter convention mainly affects the regular depreciation on basis that is not bonus-depreciated. Basis expensed under §179 is left out of the 40% test (Treas. Reg. §1.168(d)-1(b)(4)); have the tax advisor confirm how bonus-depreciated basis is counted and run the test on the full placed-in-service schedule.

What if my study is finished after I already filed a return?

A later cost segregation study can still be useful when the property was placed in service in an earlier tax year and the correction route fits section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13.

Form 3115 filed with the current-year return reports missed depreciation as a §481(a) adjustment, with no amended returns, when the property has been depreciated on two or more filed returns, or on one filed return if the taxpayer placed it in service in the tax year immediately before the year of change, the taxpayer still owned the property at the start of the year of change, and the taxpayer meets the other eligibility rules in section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13.

For a building placed in service in 2026, the cost segregation result goes on the 2026 return and no Form 3115 is needed for that current-year property under section 6.01 of Rev. Proc. 2025-23.

For a building you placed in service in 2024 or earlier and still own, Form 3115 with the 2026 return can claim the missed depreciation as a §481(a) adjustment when the eligibility rules in section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13 are met.

For a building you placed in service in 2025 with the 2025 return filed, Form 3115 with the 2026 return or an amended 2025 return filed before the 2026 return is filed are both available routes when the requirements in section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13 are met.

A prior election out of bonus depreciation cannot be undone through this automatic accounting-method change under section 6.01(1)(c)(vi) of Rev. Proc. 2025-23, so confirm the route and any prior elections with your tax advisor before filing.

Will the accelerated depreciation actually help me this year?

Accelerated depreciation helps in 2026 only if the deductions are usable under §469, §465, §461(l), and the owner’s specific taxable-income position.

A cost segregation study is worth it when three conditions hold together: the basis is large enough for the accelerated deductions to outweigh the cost of the study, the deduction is usable this year given the owner's passive-activity position, and the hold is long enough to survive recapture. All three, or the honest answer is no.
ClickDrag Finance year-end planning rule

A rental activity is passive under §469(c)(2) unless an exception such as §469(c)(7) applies, and a passive loss that passive income does not absorb is disallowed under §469(a) and carried forward under §469(b).

Under §469(i), an individual who actively participates in a rental real estate activity (a separate test from material participation, and one that requires an interest of at least 10% by value (a spouse’s interest counts) throughout the year) is exempt from the §469(a) disallowance for up to $25,000 of loss from the rental real estate activities in which the individual actively participates; the $25,000 is reduced by 50% of modified adjusted gross income above $100,000 and is gone at $150,000, and for a married individual filing separately it is $12,500, phasing out between $50,000 and $75,000, only if the spouses lived apart for the entire year, and zero if they lived together at any time during the year.

Under §469(c)(7), a taxpayer is a real estate professional only if more than one-half of the personal services the taxpayer performs in trades or businesses during the year are performed in real property trades or businesses in which the taxpayer materially participates, and the taxpayer performs more than 750 hours of services during the year in real property trades or businesses in which the taxpayer materially participates (on a joint return, one spouse must meet both tests alone); the rental loss is then nonpassive only if the taxpayer also materially participates in that rental activity, with each rental tested separately unless the election under Treas. Reg. §1.469-9(g) to treat all interests in rental real estate as one activity was made.

An activity is not a rental activity when the average period of customer use is seven days or less under Treas. Reg. §1.469-1T(e)(3)(ii)(A), or 30 days or less with significant personal services provided by or on behalf of the owner under Treas. Reg. §1.469-1T(e)(3)(ii)(B), and either loss is nonpassive only with material participation under Treas. Reg. §1.469-5T(a).

A nonpassive rental or short-term-stay loss can offset wages or other nonpassive income only when the basis rules, the at-risk limits under §465, and the excess business loss limits under §461(l) also allow the deduction.

Under §469(g), a suspended passive loss is released, meaning it is treated as a loss that is not from a passive activity, when the taxpayer disposes of the entire interest in the activity in a fully taxable transaction (one in which all gain or loss realized is recognized) to an unrelated party.

On a taxable sale at a gain, recapture applies up to the amount of that gain however long the property was held, outside the Opportunity Zone rule that, for a qualifying investment held at least 10 years with the IRC §1400Z-2(c) election, applies on a sale of the qualified opportunity fund interest: §1245 recapture on 5-year and 7-year property is ordinary income, §1250 recapture of depreciation taken above straight-line including bonus on 15-year land improvements held more than one year is ordinary income, and the remaining depreciation on those land improvements and on the 27.5-year or 39-year structure is unrecaptured §1250 gain taxed at up to 25% for a noncorporate taxpayer.

If your property is in a qualified opportunity fund or qualified opportunity zone business structure, review the timing issues in opportunity zone cost segregation because, for a qualifying investment held at least 10 years, the IRC §1400Z-2(c) election can change the result on a sale of the qualified opportunity fund interest.

What should I do now if my property may fit?

An owner considering a cost segregation study for the 2026 return typically confirms the placed-in-service date, the filing route, and the usability of the depreciation before ordering or relying on the study.

Confirm when the rental or commercial property was ready and available for its intended use under Treas. Reg. §1.46-3(d)(1)(ii).
Gather the settlement statement, construction invoices or contractor pay applications, current depreciation schedule, and a land-value source.
Ask your tax advisor to model §168(k) bonus depreciation, §168(d) conventions, §469 passive-activity limits, §465 at-risk limits, and §461(l) excess business loss limits.
Use the cost segregation qualifier to see whether your property facts suggest a study may fit.
If you are comparing providers, review best cost segregation companies for questions to ask about methodology, documentation, and property type experience.

For a calendar-year taxpayer, if the property is not placed in service by December 31, 2026, depreciation does not start on the 2026 return under Treas. Reg. §1.46-3(d)(1)(ii), so a cost segregation study may still be useful later but it will not create 2026 depreciation for a property first placed in service in 2027.

Cost segregation accelerates deductions; over the life of the building the same basis is recovered, so the right question is whether acceleration changes the return enough to matter under your facts.

Frequently Asked Questions

Does a cost segregation study have to be done on the last day of the tax year?

No, a cost segregation study does not have to be completed on the last day of the tax year, because the study must be complete before the original return that claims the reclassified depreciation is filed (a later study can still be claimed through Form 3115 or an amended return, when their conditions are met). For a calendar-year taxpayer, property placed in service by December 31, 2026 is what allows depreciation to start on the 2026 return under Treas. Reg. §1.46-3(d)(1)(ii).

Can I claim 2026 depreciation if the cost segregation study is finished after the property is ready?

Yes, 2026 depreciation can be claimed if the cost segregation study is complete before the 2026 return using it is filed and, for a calendar-year taxpayer, the property was placed in service (ready and available for its intended use) by December 31, 2026. The placed-in-service rule comes from Treas. Reg. §1.46-3(d)(1)(ii), and the depreciation categories and bonus rules come from §168 and §168(k).

Can cost segregation be claimed later with Form 3115?

Yes, Form 3115 can claim missed depreciation as a §481(a) adjustment, with no amended returns, when the property has been depreciated on two or more filed returns, or on one filed return if the taxpayer placed it in service in the tax year immediately before the year of change, the taxpayer still owned it at the start of the year of change, and the taxpayer meets section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13. For a property you placed in service in 2025 with the 2025 return filed, the amended-return route before the 2026 return is filed can also be available under those procedures.

Does bonus depreciation apply to everything in a cost segregation study?

No, bonus depreciation under §168(k) applies only to qualified property with a recovery period of 20 years or less when the acquisition and placed-in-service rules are met. The 27.5-year residential rental shell, the 39-year nonresidential real property shell, and land do not qualify for bonus depreciation under §168(k).

Can an extension give more time to finish a cost segregation study?

Yes, an extension can give more time to finish a cost segregation study, because the study needs to be complete only before the return that claims the depreciation is filed, and an extension (Form 4868 for an individual, Form 7004 for a partnership, S corporation or C corporation) is an extension of time to file, not to pay. For a calendar-year individual, the 2026 individual return is due April 15, 2027, and an extension on Form 4868 moves only the filing date, so the cost segregation study then needs to be complete before the extended 2026 return that claims the depreciation is filed, and any tax owed is still due by April 15, 2027.

Does a Cost Segregation Study Have to Be Finished for 2026 Depreciation?