IRS Form 3115 for Missed Rental Depreciation: How the Catch-Up Works

TL;DR: If you bought a rental years ago and never had a cost segregation study, IRS Form 3115 lets you claim the depreciation you missed on one current return, without amending old ones. It works because depreciating short-life components over the building's 27.5 or 39 years on two or more returns counts as an accounting method, and you fix a method by changing it. The catch-up amount, called a Section 481(a) adjustment, goes on the return for the year of change. If you have filed only one return with the old depreciation, the fix is usually an amended return instead.

Why can't I just amend my old returns?

Because after two returns, the IRS no longer treats the depreciation as an error. It treats it as your accounting method.

Publication 946 (2025) says you adopt a method of accounting for depreciation "by using the same impermissible method of determining depreciation in two or more consecutively filed tax returns." Lumping carpet, cabinets, parking lots and site lighting into the 27.5 or 39-year building is an impermissible method once those items qualify for shorter lives. Treasury Regulation 1.446-1(e)(2)(ii)(d)(2)(i) treats "a change in the depreciation or amortization method, period of recovery, or convention" as a change in method of accounting. So the fix is Form 3115, not an amended return.

Amending would also leave money on the table. A refund claim generally has to be filed within three years of filing the return or two years of paying the tax, whichever is later, under Section 6511(a). A duplex bought in 2019 has deductions from years that route can no longer reach.

One exception runs the other way. If the old depreciation is on only one filed return, you generally have not adopted a method yet, and an amended return is the usual fix. Rev. Proc. 2025-23 limits this automatic change to property the taxpayer depreciated the impermissible way "in at least two taxable years immediately preceding the year of change."

How does the Section 481(a) catch-up work?

It brings every missed dollar forward into one year. An engineering-based cost segregation study tells you what each component should have been depreciated over. Your preparer figures the total depreciation you were allowed from the day the building was placed in service, subtracts what you actually claimed, and the difference is the Section 481(a) adjustment.

When that difference is in your favor, Rev. Proc. 2015-13 section 7.03(1) sets the adjustment period at "one taxable year (year of change) for a negative § 481(a) adjustment." In plain English, the whole catch-up is deducted on the year-of-change return. No old returns get reopened.

A few rules come with it. The change is automatic, and the Form 3115 instructions say "No user fee is required for a Form 3115 filed under the automatic change procedures," but only if you meet the eligibility rules. You generally have to own the property at the start of the year of change. The original form is attached to a timely filed return, including extensions, and a signed copy goes to the IRS in Ogden, Utah. Form 3115 itself runs eight pages, so expect it to take real preparation time.

A timely automatic filing also brings audit protection. Under Rev. Proc. 2015-13 section 8.01, the IRS generally will not require a change for the same item in earlier years. That protection is worth having, and the best support for the numbers is still a well-documented study.

How do you make Form 3115 easier for your tax professional?

Hand them a complete package. Form 3115 asks for a description of the present and proposed methods, the governing citations, and the 481(a) computation. Many tax professionals file only a few of these a year, and the requests tend to arrive during filing season.

A study that comes with a clear 481(a) schedule, and ideally a draft Form 3115, turns their job into reviewing and applying judgment rather than building from scratch. Some cost segregation providers include that draft with the engineering report. Ask before you engage one.

Is a look-back study worth it?

Often, yes. For a building you have owned for years, Form 3115 is the standard IRS route to recover depreciation you were always entitled to, in one year and without reopening old returns. Whether the catch-up is worth it depends on the building, on how long you have held it, and on whether you can use the deduction. I walked through the numbers in our episode on look-back cost segregation studies, and the written version is in the look-back study guide.

If you own a building you have never had studied, the no-cost analysis estimates what a look-back study would find and what it would be worth to you. No obligation and no pitch. If a study will not pay for itself on your property, I will say so. Book a time at calendly.com/david-wiener/cs or call 770-224-8504, option two. Cost segregation, 179D and R&D credit studies are delivered through my relationship with CSSI (Cost Segregation Services, Inc.).

This article is educational and is not tax, legal, or accounting advice. Every situation is different; work with a qualified tax professional before acting on any strategy described here.