A section 481(a) adjustment is the mechanism that lets a property owner claim years of missed depreciation in a single tax year after a cost segregation study reclassifies a building they already own. If your CPA has mentioned Form 3115 or a “catch-up deduction,” this is the number in question, and how it is computed decides how much lands on this year’s return.
As co-founder of Seneca Cost Segregation and a real estate investor myself, I’ve worked with many owners who order a study on a building they bought years ago and then want to know exactly how the recovered depreciation shows up. What we see consistently is that owners expect the engineering to be the hard part, yet most of their questions end up being about the 481(a) figure.
Below, I cover what the adjustment is, when a study triggers it, how the number is calculated and reported, and what can limit the benefit in a given year.
TL;DR: Section 481(a) Adjustment
- ●Years of missed depreciation, one deduction: a 481(a) adjustment rolls every prior year’s shortfall into the year you file Form 3115, with no amended returns.
- ●A negative adjustment is deducted all at once: a catch-up that lowers taxable income is taken in full in the year of change, while an income-increasing adjustment is spread over four years.
- ●The math compares two totals: depreciation you actually claimed versus depreciation allowable under the corrected classes, including bonus at the rate in force when the building was placed in service.
- ●In our example, $359,388 comes back in one year: $400,000 of reclassified components on a building placed in service in 2022 produce that negative adjustment on a 2026 return.
- ●No advance approval or user fee: a depreciation reclassification is an automatic change filed under DCN 7, with a signed copy sent to the IRS in Ogden.
- ●Passive rules and state add-backs decide what you use this year: the deduction is the same size, but how much of it offsets your income depends on your activity status and your state.
What a Section 481(a) Adjustment Does
Section 481(a) exists so that changing how you account for an item never makes income or deductions vanish or count twice.
The statute itself, Internal Revenue Code section 481, applies the adjustment in the year of the change and limits it to what is needed “solely by reason of the change in order to prevent amounts from being duplicated or omitted.” For a building, the amounts at stake are the depreciation deductions you would have claimed had the components been classified correctly from day one.
Cost segregation sits squarely inside this rule. The Treasury regulations on accounting methods include an example in which a taxpayer runs a cost segregation study, finds building components that should have been 5-year property, and is told the reclassification is a change in method of accounting that “results in a section 481 adjustment.”
When a Cost Segregation Study Triggers the Adjustment
Depreciation is treated as a method of accounting, so moving components to shorter recovery periods counts as a method change once the old treatment has become your method.
The Two-Return Rule
Under Revenue Procedure 2015-13, treating an item the same way on two or more consecutively filed returns establishes a method, even when that treatment was wrong. A building depreciated as one 39-year or 27.5-year asset for two filing seasons has therefore adopted that method, and the fix runs through Form 3115 with a 481(a) adjustment.
If an item is handled correctly on the first return that reflects it, the method is adopted right away.
Property Placed in Service Last Year
A building placed in service in the tax year just before the year of change has appeared on only one return. The current IRS list of automatic changes lets you correct it either on Form 3115 or by amending the placed-in-service return, provided the amendment goes in before you file the following year’s return.
Our guide to cost segregation on a recently purchased building walks through that timing decision in more detail.
What a Method Change Cannot Fix
The automatic procedure corrects how depreciation was computed. You cannot use it to make a late election or to revoke a timely one, including an election out of bonus depreciation, and those requests go to the IRS as a letter ruling instead.
The change also covers only property you still own at the beginning of the year of change. Assets disposed of earlier fall under a separate automatic change with its own rules.
How to Calculate the Adjustment
Section 6.01 of Revenue Procedure 2025-23 sets the rule: the adjustment equals the total depreciation taken into account under your present method minus the total depreciation allowable under the proposed method, for open and closed years before the year of change.
Closed years count too. A building held for a decade catches up the full decade, well past the years still open for amendment.
Depreciation Already Taken
Start with what the existing schedule actually deducted on the components the study identifies, year by year from the placed-in-service date. On a building depreciated as a single asset, that is the straight-line amount attributable to those components under the 39-year or 27.5-year tables.
Depreciation Allowable Under the Corrected Method
Next, recompute those same components under their correct classes, methods, and conventions for every prior year. Allowable depreciation includes bonus depreciation for the year the property was placed in service whenever the property qualified and no timely election out was made for that class.
We see this framing consistently from clients: they expect a building bought years ago to catch up at today’s 100% rate. The rate that counts is the one in force for the placed-in-service year, and our breakdown of how bonus depreciation changed under the One Big Beautiful Bill shows where the January 19, 2025 cutoff falls.
A Worked Example
Here is a simplified, hypothetical case. A nonresidential building was acquired and placed in service in January 2022 with $1,600,000 of depreciable basis and depreciated as one 39-year asset through 2025; a study completed in 2026 moves $400,000 of that basis into 5-, 7-, and 15-year property.
Qualified property acquired and placed in service after September 27, 2017, and before January 1, 2023, received 100% bonus depreciation, so the full $400,000 was allowable in 2022. The remaining $1,200,000 simply stays on its 39-year schedule.
How the Sign Sets the Spread Period
Once the number is computed, its direction decides when it reaches your return.
Negative Adjustments Land in One Year
A negative adjustment reduces taxable income, and Revenue Procedure 2015-13 takes it into account entirely in the year of change. That is the usual result for a cost segregation catch-up, since the corrected method allows faster depreciation than the one you were using.
When a Catch-Up Comes Out Positive
A positive adjustment means the old method claimed more than was allowable, which can happen when an earlier study put structural items in a short-life class or when an asset moves from 5-year to 7-year property. Positive amounts are spread over four years, or over two if you are under examination and no exception applies, and an adjustment under $50,000 can be taken in one year by election.
How to Report the Adjustment on Form 3115
Form 3115, Application for Change in Accounting Method, carries both the change and the 481(a) amount, which is reported in Part IV with a statement showing how it was computed.
DCN 7 and the Automatic Change Procedure
A change from an impermissible to a permissible depreciation method is designated automatic change number 7 on the current list. Automatic changes need no advance consent and carry no user fee, which keeps the filing manageable for most owners.
Your CPA enters the change number, attaches the computation, and reports the adjustment on the return for the year of change. Our article on how CPAs integrate cost segregation results covers the handoff from finished study to filed return.
The Original and the Signed Duplicate
The Form 3115 instructions require two filings for an automatic change. The original is attached to your timely filed return for the year of change, including extensions, and a signed copy goes to the IRS in Ogden, Utah, no earlier than the first day of the year of change and no later than the date you file the original.
Audit Protection for Prior Years
A timely filed Form 3115 generally means the IRS will not require you to change the same item for years before the year of change. Revenue Procedure 2015-13 lists exceptions, most notably for taxpayers already under examination, so confirm your status with your CPA before filing.
What Can Limit the Benefit
The size of the adjustment and the tax you save this year are two separate questions.
Passive Activity Rules
IRS Publication 925 treats a rental activity as passive unless you materially participate as a real estate professional. A large catch-up on a rental building can therefore be suspended and carried forward when you have no passive income to absorb it, and our guide to whether cost segregation can offset W-2 income explains the statuses that change that answer.
State Bonus Depreciation Add-Backs
States that decouple from federal bonus depreciation may not accept the bonus portion of a federal catch-up as filed. The Minnesota Department of Revenue, for example, applies its 80% bonus add-back to the part of a section 481 adjustment that relates to bonus depreciation, then allows 20% of the add-back back in each of the next five years.
Recapture When You Sell
Faster depreciation now can mean more recapture when you sell, and our breakdown of the depreciation recapture tax rate shows how each property class is taxed.
How Seneca Supports the 481(a) Figure
At Seneca, here is what the cost segregation study process looks like for a property you already own and want to catch up.
Property Records and the Existing Schedule
We start with your closing documents, the placed-in-service date, and the depreciation schedule your CPA has been running. That schedule is the depreciation-taken side of the 481(a) math, so we ask for it early.
Onsite or Virtual Tour
You choose whether our engineers walk the property in person or tour it virtually. Many commercial owners choose onsite, virtual works well for most residential properties, and our page on virtual property tours for cost segregation explains how the remote option runs.
Component Breakdown and Report
Our engineers break the property into every component it contains, each with a cost and recovery class, which gives your CPA the allowable side of the calculation. Our Head of Engineering signs off on every study before it reaches your CPA, and with timely collaboration from you, we deliver in 5 to 10 business days.
Mistakes That Shrink or Delay the Catch-Up
Most problems with a 481(a) adjustment are procedural, and each one has a simple correction.
- ●Amending old returns instead of filing Form 3115: once the old treatment appears on two consecutive returns, amended returns are the wrong tool and can be rejected; file the method change with your current return instead.
- ●Skipping the signed duplicate: the automatic procedure needs the copy sent to the IRS in Ogden as well as the original on the return, so confirm your CPA has sent it within the window.
- ●Modeling the catch-up at today’s bonus rate: components placed in service in 2024 catch up at the 60% rate, so an estimate built on 100% overstates the deduction; ask for numbers tied to your actual placed-in-service year.
- ●Expecting Form 3115 to change a bonus election: the automatic change cannot add a late election out or revoke one, so settle election questions with your CPA before the study’s numbers go on the return.
Frequently Asked Questions
Below are the questions we hear most from owners and CPAs working through a 481(a) catch-up.
Why CPAs Trust Seneca With Catch-Up Studies
Seneca’s in-house engineering team does cost segregation and nothing else, and that focus shows in the reports CPAs receive for a 481(a) catch-up. Every study breaks the property into all of its components, we also perform Qualified Production Property (QPP) studies, and our Head of Engineering signs off on each report.
Your point of contact is a dedicated Project Manager backed by our Engineering team and an Advisor, so you hear real-time updates at each stage instead of chasing them. Audit defense comes with every engagement, and we have assessed 10,200+ properties with zero IRS audits triggered or lost.
To size a catch-up before you commit, try our cost segregation calculator.
Conclusion
A section 481(a) adjustment is how the tax code squares the books after a cost segregation study on a building you already own. The math compares what you deducted with what was allowable, and for most owners the gap arrives as a single negative adjustment in the year they file Form 3115.
The details still decide the result: the bonus rate for your placed-in-service year, a timely filing with its signed duplicate, and a clear view of the passive, state, and recapture effects worked out with your CPA.
If you own a building that has never been broken into its components, run it through the calculator or reach out for a free estimate, and our engineers will show you what the catch-up could look like.
