Yes. If you bought a rental property years ago and have been depreciating the whole building over 27.5 or 39 years, you can still do a cost segregation study today. A look-back study reclassifies the components retroactively, and a single accounting method change on Form 3115 captures all the missed depreciation in the current tax year. You do not amend your prior returns.

How does a look-back study work?

The mechanics have three steps. First, an engineering-based study examines the property and allocates its original cost across the correct asset classes: 5-year, 7-year, and 15-year property for the qualifying components, with the rest staying in the building's original 27.5- or 39-year bucket. Second, your tax preparer computes what depreciation you should have claimed each year under the correct classifications. Third, you file Form 3115, Application for Change in Accounting Method, and take the entire difference as a section 481(a) catch-up adjustment on the current year's return. One filing, one year, all the missed depreciation at once. (Revenue Procedure 2025-23; IRS Instructions for Form 3115)

The change is automatic. The IRS's list of automatic accounting method changes specifically covers changing from an impermissible to a permissible method of accounting for depreciation, which is exactly what a look-back cost segregation is: you were using an impermissible method (everything in the long-life bucket) and you are switching to the permissible one (each component in its correct class). Automatic means no IRS permission letter and no user fee. You attach the Form 3115 to your timely filed return and send a copy to the IRS national office.

Do I need to amend prior tax returns?

No, and you should not. Once you have used an impermissible depreciation method for two or more years, it becomes your established method of accounting, and the fix is a method change, not a series of amended returns. The section 481(a) adjustment exists precisely to prevent double-counting or omission across the change: it trues up the cumulative difference in a single year. Amending would be the wrong procedure and would forfeit the clean one-year catch-up.

What bonus rate applies to the catch-up?

This is the detail most articles get wrong. The catch-up does not automatically get today's 100% bonus rate. The section 481(a) adjustment is computed as if you had used the correct method from the beginning, which means the reclassified components get the bonus depreciation rate from the year the property was placed in service. A property placed in service in 2022 catches up at the 100% rate from that year. One placed in service in 2024 catches up at 60%. A property placed in service in the first days of 2025 catches up at the 40% phase-down rate. The One Big Beautiful Bill Act's permanent 100% rate applies to qualifying property acquired after January 19, 2025, so it governs new acquisitions and recent purchases, not decade-old ones. (IRS Notice 2026-11)

This is still powerful. Even at a 60% catch-up rate, a look-back study on a property placed in service in 2024 pulls forward the majority of the short-life depreciation into the current year.

When does a look-back study pay off?

The economics come down to three variables:

• Property value. Studies typically run in the low thousands of dollars (commonly quoted in the $3,000 to $5,000 range for a straightforward residential rental), so the property needs enough depreciable basis for the accelerated deductions to dwarf the fee. Higher-value properties clear this bar easily.

• Hold period. You should plan to hold the property for the medium to long term. Selling soon after a study triggers depreciation recapture that claws back the benefit, and the transaction costs of a sale erase the timing advantage.

• Usability of the loss. The study creates a bigger paper loss. The passive activity rules still decide whether that loss offsets your other income this year. Pair the study decision with your REPS or short-term rental position, not in isolation.

When all three point the right way, a look-back study is one of the highest-return tax moves available to an existing landlord. When any of the three fails, say a planned sale next year, or a fully passive position with no passive income, the honest answer is to skip it.

Updated October 14, 2026.

This article is free educational content, not tax advice for your specific situation. If you want a plan built around your actual numbers, that is what our paid tax planning engagements do.