Retroactive Look-Back Cost Segregation Study

By Jason Watson, CPA
Posted Sunday, July 12, 2026

Is there more to a cost segregation study? Yes, there is! So, we have two look-back cost segregation situations-

• You do a cost segregation study in the current year and would like to “catch up” depreciation that was not taken on previous tax returns.
• You do a cost segregation study in the current year for a prior year and would like to apply accelerated depreciation to that earlier year with a tax return amendment, assuming an amendment is allowed.

What’s the difference between a look-back cost segregation study and retroactive cost segregation study? Probably not much, but we’ll split some hairs. Let’s consider a retroactive study to be one where you are wanting to restate depreciation on a prior year tax return. Next, a look-back study is where you are wanting to claim a catch-up depreciation deduction in the current year. The IRS references look-back in their IRS Publication 5653 Cost Segregation Audit Techniques Guide (ATG).

Careful. “Retroactive” does not automatically mean “amend.” If a depreciation method has already been adopted, the correction is generally a method change using Form 3115, not a choose-your-own-adventure tax return amendment. Fun books. Bad tax procedure. The refund statute matters, but the accounting method rules might matter more. We dig into this in a bit.

Cost Segregation Examples

Why would you want to pick the second option above (the amendment or retroactive option)? Perhaps your income was sky high in 2023 and that big marginal tax bracket could use a little dent. Perhaps that was the only year you qualified as a real estate professional or could use the short-term rental loophole, and you just discovered this thing called cost segregation and accelerated depreciation, but your rental property is now long-term.

What if it is the current tax year, and you purchased a rental property several years ago? Assuming you could deduct the depreciation expense to create a reduction in taxable income, you might be unable to claim a refund for the older year because of the 3-year claim for refund statute of limitations. So, this might be silly, right? You are likely forced to use look-back.

But the refund statute is only one problem. The accounting method rules are another.

A depreciation method is generally adopted when you use the same depreciation treatment on two or more consecutively filed tax returns for the same item of property. In plain English, if you keep depreciating the asset the wrong way, the IRS eventually treats that wrong way as your accounting method. Lovely.

Once that happens, you generally do not fix the problem by simply amending an open year. You request a change in accounting method using Form 3115 and calculate an IRC Section 481(a) adjustment so the missed depreciation is caught up in the year of change.

Same situation as above, but you perform a retroactive cost segregation study for the 2023 tax year including the tax return amendment. Now we are cooking with gas (maybe). 2023’s tax returns were due April 15, 2024, so you have until April 15, 2027, to claim a refund, or October 15, 2027, if you extended your tax returns. You also have some housekeeping concerns in 2024 and 2025 since the depreciation taken would now be incorrect based on the new depreciable basis going forward from the 2023 amended tax return. Housekeeping is a nice way of saying tax return amendments are probable.

What if you don’t feel like amending your prior-year tax return? Perhaps you believe amendments increase audit risk (spoiler alert, they don’t)? Perhaps you don’t like the housekeeping problems with depreciation in the years that followed. Better yet, perhaps the current year is a much higher income year, and a big old depreciation deduction sounds tasty. What can be done?

By using Form 3115 Application for Change in Accounting Method with an IRC Section 481(a) adjustment, you may be able to catch up the depreciation that should have been claimed under the bonus depreciation rules for the original placed-in-service year.

Read that again! You may be able to apply the bonus depreciation percentage from the original placed-in-service year on the current-year tax return through the IRC Section 481(a) adjustment. In other words, the bonus percentage follows the original placed-in-service year, not the year you finally get around to ordering the cost segregation study. There are more mathematical gymnastics since the property eligible for bonus depreciation has been partially depreciated. Also, if you opted out of bonus depreciation in the past, this becomes problematic.

For example, 2022 was sexy at 100% whereas 2026 is 20% (assuming a property not covered by OBBBA). This can work to your advantage.

Sidebar: Many states do not follow the federal bonus depreciation rules. States such as California, New York, New Jersey and Hawaii require taxpayers to add back bonus depreciation and recover it over several years. This means a large federal deduction may create little or no immediate state tax benefit.

Another option is to not take bonus depreciation. Rather, you take the accumulated accelerated depreciation for 2023, 2024 and 2025 plus 2026 on your 2026 tax returns. This is an acceleration in a sense since you are carving out 5-year property (for example), but taking most (80%, 4 out of 5 years) from the back end of the depreciation schedule on today’s tax return.

Keep in mind that you can elect out of bonus depreciation for certain classes of property. In the example above, you could opt-out for 5-year property since you mostly don’t need it, and retain bonus depreciation for 7-year and 15-year property.

Look-Back Cost Segregation Mechanics

Ok, we’ve tossed around some terms like Form 3115 and IRC Section 481(a). What’s the difference, and how are they used together?

Form 3115 Application for Change in Accounting Method is used to request permission from the IRS for a change in an accounting method (such as cash to accrual) including changes to your depreciation accounting method. Specifically, if you’ve been historically depreciating a 5-year asset over 39.0 years, and you now want to accelerate depreciation, you need permission from the IRS.

Since this request is mostly rubber-stamped by the IRS, you then use IRC Section 481(a) to adjust depreciation to the correct number on your tax returns. In other words, this adjustment is more of a do-over or mulligan where you say, “had we depreciated correctly from the beginning, it would be this new number here that we conveniently want to deduct today.”

Quick summary- Form 3115 asks for permission to change and IRC Section 481(a) states that proper taxable income computation requires omitted or duplicate depreciation amounts to be accounted for. What is the IRC Section 481(a) adjustment thing? Here is the code-

A few options to summarize-

• Amend the prior year tax return since income was significantly higher that year, or you can only support real estate professional status or short-term rental loophole that year.

• Use Form 3115 plus the IRC Section 481(a) catch-up on today’s tax return which conveniently has two options- use bonus depreciation or elect out of bonus depreciation.

As you can see, there is a nice tax planning opportunity here and perhaps even some tax arbitrage given income fluctuations. Keep in mind that generally you will be going back to the in-service date of the rental property (ready and available for occupancy, and held out for rental use through advertising and related efforts) to calculate the amount of depreciation that should have been taken (accumulated) between then and now.

Could you file Form 3115 but not use IRC Section 481(a) to adjust depreciation? Yes. Maybe. Kinda rare. Sure, there is a world where you want (need) to change depreciation today for the future, and do not need or perhaps you are not eligible for a look-back catch-up adjustment.

Sidebar: Changing from 27.5 to 39.0 years for depreciation, or vise-versa, does not require filing Form 3115. A change in computing the depreciation allowance in the year of change for property is not a change in method of accounting according to Treasury Regulations Section 1.168(i)-4(f). Who knew? See our section on switching depreciation for more information.

The Ultimate Tax Arbitrage (Passive to Non-Passive)

Let’s look at a sexy piece of tax arbitrage using a look-back study and Form 3115. What happens if the character of your rental property changes?

Imagine you purchase a rental property in 2022. For 2022, 2023, and 2024, it operates as a traditional long-term rental. Because you have a day job with high income and you are not a real estate professional, any losses generated by the property are suspended due to passive activity loss limitations. Doing a cost segregation study during those years wouldn’t provide immediate tax relief; it would just build up a larger bucket of suspended passive losses.

But in 2025, the long-term tenant moves out. You furnish the property and pivot to a short-term rental. In 2026, you manage it yourself, keeping the average stay to 7 days or less and meeting the 100-hour material participation test (or any of the 7 tests). Suddenly, your rental qualifies for the short-term rental loophole, meaning the activity is now non-passive.

Here is where the tax arbitrage happens. In 2026, you commission a cost segregation study going back to the 2022 purchase date. You file Form 3115 with your 2026 tax return to claim the missed depreciation which also happens to include 100% bonus depreciation from 2022.

Because the IRC Section 481(a) adjustment is deducted entirely in the year of the accounting method change, the passive or non-passive character of the deduction is determined based on the activity’s status in that year per IRC Section 469. Since 2026 is the year of change, and the rental property in our example is non-passive in 2026 as a qualifying short-term rental, the entire catch-up depreciation deduction is treated as non-passive.

The tax law does not track the passive character of the underlying years when a Section 481(a) adjustment is taken. It simply treats the entire adjustment as a deduction in the year of change.

Boom! You just pulled massive deductions from passive years where they would have been trapped, and dropped them directly onto your current-year tax return to offset your W-2 or active business income. No amendments required, and the bonus depreciation percentage still follows the original placed-in-service year. For a rental purchased and placed in service in 2022, that means you might capture 2022’s 100% bonus depreciation rate even though you were late to the cost segregation party.

Sidebar: The One Big Beautiful Bill Act (OBBBA) restored 100% bonus depreciation, Yes, but only for rental properties acquired and placed into service after January 19, 2025. It does not retroactively fix previous years such as 2024 and 2023 when bonus was less than 100%. You must use the tax law that applied when the rental property, or its cost-segregated components, was originally placed in service.

The big takeaway with all this is- The bonus depreciation percentage is based on when the rental property was acquired and placed into service, and not when the cost segregation study is performed or when Form 3115 is filed!

Look-Back Cost Segregation Study For 1 Year

What about going back just one year? You purchase a rental property in Year 1 and naturally start depreciating it using conventional methods. You learn about cost segregation in Year 2 after filing your Year 1 tax return. Now what? Are you hosed because you technically have not established an accounting method yet (spoiler alert, the normal accounting method rule generally looks for two years)? Nope.

The short answer is the one above: file Form 3115, Application for Change in Accounting Method, and apply an IRC Section 481(a) adjustment. But there is a technical difference that most tax professionals are unaware of. To request a change in accounting method, in this case for depreciation, you normally need to have at least two years of using an accounting method to have an established method. If you have only depreciated the rental property on one tax return, you might not have the requisite two years necessary to apply for a traditional change in accounting method. Historically, many practitioners viewed your only recourse as amending the prior return to deduct the unclaimed depreciation. Yuck.

However, according to the over 400 pages found in IRS Revenue Procedure 2025-23 (yes, it is updated annually),

(b) Taxpayer has not adopted a method of accounting for the item of property. If a taxpayer does not satisfy section 6.01(1)(a)(i) of this revenue procedure … because this item of property is placed in service by the taxpayer in the taxable year immediately preceding the year of change the taxpayer may change from the impermissible method of determining depreciation to the permissible method of determining depreciation for the 1-year depreciable property by filing a Form 3115 for this change, … Alternatively, the taxpayer may change from the impermissible method of determining depreciation to the permissible method of determining depreciation for a 1-year depreciable property by filing an amended federal income tax return.

Tilt! To put this in simple terms, there is an exception in Year 2 where you can file Form 3115 even though you might not have technically established a two-year depreciation method yet. Alternatively, an amended return might also be available for that same property.

As mentioned elsewhere in this section, once the same wrong depreciation method shows up on two tax returns, Form 3115 is generally the required path, not an amendment. This is why timing matters: the correction tool changes depending on how many tax returns have already carried the error.

Sure, in the example above, you are stuck with the bonus depreciation percentage from the original placed-in-service year. OBBBA brought 100% bonus depreciation back for qualifying property acquired and placed in service after January 19, 2025, but look-back cost segregation does not magically rewrite history. You must use the tax law that applied when the rental property, or its cost-segregated components, was originally placed in service. That might be 100%, 80%, 60%, 40%, 20%, or whatever number Congress coughed up for that year.

Opted Out of Bonus Depreciation Revisited

As we mentioned in a previous section, bonus depreciation election is assumed. If you elect to opt-out of bonus depreciation for some reason (and there are some narrow ones), you can revoke the election to opt out which is like a triple negative. How about this? You can amend your tax returns to claim and deduct bonus depreciation under IRS Revenue Procedure 2020-50.

This is generally good news but here is the bad news- a taxpayer who opted out may revoke that election by filing an amended return only if-

• the initial election to opt out was made on a timely filed tax return, and

• the amended tax return is filed within six months (excluding extensions) of the original tax return’s due date.

Yuck! However, there might be relief by making a request using Form 3115 Application for Change in Accounting Method. More discussion is likely required with your cost segregation buddies at WCG CPAs & Advisors.

Form 3115 does not technically revoke the prior election to opt out of bonus depreciation. Instead, it asks the IRS for permission to change the taxpayer’s depreciation method. If approved, the taxpayer adopts the new method going forward and adjusts prior depreciation through the IRC Section 481(a) catch-up adjustment, which can allow the depreciation that should have been taken in earlier years to be deducted in the current year.

Retroactive Cost Segregation Summary

Bonus depreciation is determined by when the property was placed in service, not when or how you claim the deduction. In other words, if bonus is 100% today (play along), but 60% when you placed the rental into service (for the 2024 tax year), you are stuck with 60%. Ok, we’ve beat that up a million times to Sunday.

But here is a correction path table in case you slept through class.

Scenario	Depreciation Method Adopted?	Typical correction path
One return filed using the incorrect depreciation method	Generally no	Amend or Form 3115 if current guidance allows
Two or more returns filed using the incorrect depreciation method	Generally yes	Form 3115
Look-back cost segregation after multiple filed years	Generally yes	Form 3115

If Form 3115 is used, the catch-up depreciation is generally handled through an IRC Section 481(a) adjustment in the year of change. Fancy phrase. Simple idea. You deduct today what should have been deducted earlier, while preventing duplicate or omitted depreciation.

Bonus depreciation opt-out issues are a different animal because those involve elections, not just depreciation method corrections. We discuss that separately above.

Generally, filing Form 3115 is preferred, and often required, for look-back cost segregation corrections for a handful of reasons-

• It is usually more economical in terms of professional fees. There goes our bar fund.
• It avoids housekeeping troubles with “sandwiched” tax returns where multiple years might need to be amended.
• It reduces state tax return headaches, although state conformity must still be reviewed.
• Once an accounting method has been adopted, amending prior returns is generally not the correction path unless a specific rule allows it.

The three-year refund statute matters, but it is not the only limitation. The bigger issue is whether you have already adopted an impermissible depreciation method. As mentioned previously, a one-year filed return case may allow an amended return or Form 3115, and an election issue such as opting out of bonus depreciation can have its own relief rules. More discussion is required before choosing the correction method.

The big takeaway with all this is- The bonus depreciation percentage is based on when the rental property was acquired and placed into service, and not when the cost segregation study is performed or when Form 3115 is filed. In other words, if your rental property was placed in service (ready and available for occupancy, and held out for rental use through advertising and related efforts) in 2023, you are limited to 80% bonus depreciation. If you fired up the rental in 2024, then 60%. But, if you had it placed in service in 2022, then you get to use that year’s bonus depreciation which was 100%.

The good news is that 100% bonus depreciation is back for the 2025 through 2030 tax years thanks to the One Big Beautiful Bill Act (OBBBA) that was signed into law in July 2025. The 80% and 60% years were the dip in between.