The Section 481(a) Adjustment: How Catch-Up Depreciation Works on a Look-Back Study
The Mechanism That Makes Look-Back Studies Work
The most common question about cost segregation on a property you already own is some version of: have I missed my chance? The answer is no, and the reason is a provision most owners have never heard of.
Section 481(a) governs what happens when a taxpayer changes an accounting method. Rather than requiring you to go back and redo every affected prior year, it requires a single cumulative adjustment in the year of change, computed as the difference between what you actually deducted and what you would have deducted had the new method always been in place.
Applied to depreciation, that means an owner who has been depreciating a building straight-line for six years can adopt the correct component-level classifications, compute the entire six years of missed acceleration, and deduct all of it in the current year. Not spread over six years. All of it, in one year.
Why This Is a Method Change Rather Than an Error Correction
The distinction matters. Correcting an error generally requires amending the return for the year the error occurred, and amended returns are subject to the statute of limitations, typically three years.
Depreciation is different. Under the regulations, using an impermissible method of depreciation for two or more consecutive years establishes a method of accounting. Changing from that method to a permissible one is a change in accounting method, which goes on Form 3115 rather than an amended return.
That has two consequences owners care about. First, no amended returns. You do not reopen prior years, you do not disturb prior filings, and you do not need your prior preparer's cooperation. Second, no lookback limit. Because you are not amending anything, the three-year statute is not the constraint. A study on a property placed in service in 2011 can capture every year of missed depreciation since 2011.
There is a wrinkle for property held less than two tax years. If you have used the original method for only one year, you have not yet established a method of accounting, and an amended return may be the correct route instead. That timing question should be settled before filing.
How the Catch-Up Is Actually Computed
Consider a commercial property placed in service in January 2021 with a $3,000,000 depreciable basis. Under the 39-year straight-line schedule the owner has been deducting roughly $76,923 per year. Through the end of 2025, five years of deductions total approximately $384,615.
A study performed in 2026 determines that $900,000 should have been classified as 5-year and 15-year property. Had that classification been in place from the start, the owner would have claimed the applicable bonus depreciation on that $900,000 in 2021 plus depreciation on the remaining $2,100,000 shell over 39 years. The cumulative correct depreciation through 2025 is substantially larger than $384,615.
The difference between the two cumulative figures is the Section 481(a) adjustment. Because it is a favorable adjustment, meaning it decreases taxable income, it is taken entirely in the year of change. Unfavorable adjustments that increase income are generally spread over four years, but that is not the situation in a cost segregation look-back.
One important constraint: the bonus depreciation rate used in the computation is the rate that applied in the year the property was placed in service, not today's rate. A 2021 property uses the 2021 rate. A look-back recovers what you were entitled to under the law then.
Filing Mechanics
The change is made on Form 3115, Application for Change in Accounting Method, filed under the automatic consent procedures. Because it is automatic, no advance IRS approval and no user fee are required. A copy of the form is attached to the timely filed return for the year of change, including extensions, and a duplicate is filed separately with the IRS.
The form requires a description of the present and proposed methods, the computation of the Section 481(a) adjustment, and the designated change number for the depreciation change being made. The cost segregation study is the supporting documentation behind the numbers on the form, and it should be retained rather than attached.
The deadline is the return due date including extensions for the year of change. This is a real constraint. A study started in late March for a calendar-year taxpayer may not be complete in time to file by the original deadline, which is one reason extensions are common in the year an owner adopts a study. Our post on Form 3115 look-back cost segregation covers the filing sequence in more detail, and AE Tax Advisors addresses the preparer side in their Form 3115 guide.
The Question That Determines Whether It Is Worth It
A large catch-up deduction is only useful if you can absorb it. If the property is a passive rental and you have no passive income, the entire 481(a) adjustment becomes a suspended passive loss carrying forward. The study still has value, because the loss frees up when you have passive income or dispose of the property, but the cash benefit is deferred.
This is why timing a look-back deliberately often beats doing it as early as possible. An owner who expects to sell another property, take a large K-1 distribution, or qualify for real estate professional status in a particular year may be better served placing the catch-up in that year. Our post on passive activity loss rules and cost segregation works through the analysis.
Running the Numbers on Your Property
Stratum performs look-back studies on properties placed in service in any prior year, including the cumulative computation your CPA needs to complete Form 3115. If you have owned a property for more than a year and never had a study, the catch-up is usually the single largest deduction available to you.
Request a free estimate or book a call with your placed-in-service date and current depreciation schedule.