Where do I file Form 3115?

For an automatic change, you attach a copy to the timely filed return for the year of change and mail a duplicate copy to the IRS at the address in the current form instructions. For a non-automatic change, you file the form with a user fee by the last day of the year of change. The addresses change, so always check the current instructions.

Why does cost segregation require Form 3115?

A cost segregation study performed after a property has been in service reclassifies assets that were previously depreciated over a longer life. That is a change in accounting method, so Form 3115 is required, and the section 481(a) adjustment lets you claim all the missed depreciation in the year of change rather than amending prior returns.

What is a section 481(a) adjustment?

It is the cumulative catch-up that prevents income from being duplicated or omitted when you change methods. A negative adjustment, meaning additional deductions, is generally taken entirely in the year of change. A positive adjustment, meaning additional income, is generally spread over four years.

Do I need to amend prior returns instead of filing Form 3115?

Generally no, and often you cannot. A change in accounting method is made prospectively with a catch-up adjustment, not by amending. Amending is appropriate for correcting an error such as a mathematical mistake, while a method change addresses a consistent treatment applied over more than one year.

Is there a fee for filing Form 3115?

Automatic changes under the published list of designated change numbers carry no user fee. Non-automatic changes require advance IRS consent and a user fee that is published annually. Most depreciation and cost segregation changes fall in the automatic category.

IRS Form Guide

Form 3115

The form that lets you claim years of missed depreciation in a single year, without amending a single prior return.

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A guide by Taxstra Tax & Accounting · CPA-led tax strategy for business owners

Your Guide

01What a Method Change Actually Is 02The Section 481(a) Catch-Up 03Automatic Versus Non-Automatic 04Where and When to File 05Frequently Asked Questions

IRS Form Guides>Form 3115

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last updated August 15, 2026.

Quick answer

Form 3115 is the Application for Change in Accounting Method. It changes how an item is treated going forward and carries a section 481(a) adjustment that catches up the cumulative difference. It is the mechanism behind a look-back cost segregation study on a property already in service.

Form 3115 is one of the few forms in the code that can produce a very large deduction in a single year for something that happened years earlier. It exists because the tax system distinguishes between fixing an error and changing a method, and it gives the second one a forward-looking mechanism with a catch-up built in.

For real estate investors this is the machinery behind a look-back cost segregation study, which is why the form appears far more often in property planning than its name suggests.

What a Method Change Actually Is

Not an error correction, which is a different process entirely.

A method change, use Form 3115

Changing depreciation life or method
Reclassifying components after a cost segregation study
Switching between cash and accrual accounting
Changing an inventory method
Adopting a repair regulation safe harbor
Correcting a treatment applied consistently over two or more years

An error, amend instead

A mathematical mistake
Omitting a form or a transaction
Using the wrong figure in one year only
A treatment applied only once

The two year rule of thumb

A treatment used on two or more consecutive returns is generally established as a method, which means Form 3115 rather than an amended return. A treatment used once is generally an error to be amended. That distinction determines which path is available, and taking the wrong one produces a filing the IRS will not process.

The Section 481(a) Catch-Up

The reason the form is worth filing at all.

When you change methods, the cumulative difference between what you deducted historically and what the new method would have produced does not disappear. Section 481(a) reconciles it in a single adjustment.

Worked example

A property placed in service four years ago has been depreciated entirely over its long building life. A cost segregation study reclassifies a portion into shorter-lived components.

Depreciation actually claimed over four years$120,000

Depreciation the new method would have produced$480,000

Section 481(a) adjustment, negative$360,000

Claimed in the year of changeAll of it

Illustrative arithmetic only. Whether the resulting loss is usable this year depends on passive activity rules, at-risk limits, and your participation level.

Adjustment direction	Effect	Timing
Negative	Additional deductions	Generally taken entirely in the year of change
Positive	Additional income	Generally spread over four years

Watch Out

A large deduction is not the same as a usable one

A negative 481(a) adjustment creates a deduction, not necessarily a current-year tax benefit. Passive activity loss rules can suspend the entire amount for a taxpayer who does not materially participate. Confirming that the loss will actually be usable is the analysis that should precede a study, not follow it.

Automatic Versus Non-Automatic

Two consent procedures with very different burdens.

	Automatic	Non-automatic
Advance IRS approval	Not required	Required before the change
User fee	None	Yes, published annually
Identified by	A designated change number from the published list	A written request describing the change
Deadline	With the timely filed return for the year of change	By the last day of the year of change
Typical use	Depreciation and cost segregation changes	Unusual or taxpayer-specific methods

Taxstra CPA Tip

Taxstra Tip

The non-automatic deadline is genuinely unforgiving: it falls on the last day of the tax year of the change, not at filing time. A taxpayer who realizes in March that they wanted a non-automatic change for the prior year has already missed it. Most depreciation changes are automatic, which is why the distinction rarely bites in practice, but it is worth confirming before assuming.

Where and When to File

Two copies for an automatic change, and the addresses move.

Copy one, attached to the return

Include Form 3115 with the timely filed original return, including extensions, for the year of change.

Copy two, mailed separately

A duplicate copy goes to the IRS address specified in the current form instructions. Filing only the attached copy is a common and avoidable defect.

Check the current instructions for the address

The filing address has changed more than once, and the correct one depends on whether you file by mail or private delivery service. Never rely on a remembered address.

Keep the supporting study with your records

A cost segregation engagement should produce an engineering-based report. That report is the documentation supporting the reclassification if the return is examined.

In practice, most Form 3115 filings for individuals arrive through a cost segregation engagement. The mechanics of the study are in the cost segregation guide, the baseline it accelerates against is in the rental depreciation guide, and commercial property has its own longer schedule covered in the commercial depreciation guide. Choosing a provider capable of producing a defensible study is covered in the provider comparison, and the car wash example shows an asset class where the reclassification percentage is unusually high.

Own a Property You Have Held for Years Without a Cost Seg Study?

A look-back study plus Form 3115 can release years of missed depreciation into a single year. Whether it is worth doing depends on your facts. The initial consultation is free.

Frequently Asked Questions

Form 3115 is the Application for Change in Accounting Method. It is used to change how you account for an item of income or expense, most commonly depreciation. It also carries the section 481(a) adjustment, which catches up the cumulative difference between the old method and the new one.

Depreciation Timing Is the Largest Lever in Real Estate

Cost segregation, bonus depreciation, and the rules that decide whether the losses are usable this year are where Taxstra does its most valuable real estate work. Book a free initial consultation.

Next Steps

Filing it yourself is fine. Optimizing it is where the money is.

Getting the form right keeps you out of trouble. The strategies below are what actually lower the bill.

Want a CPA to run the numbers for you?

Free 30-minute call with a Taxstra CPA. No pressure, just the math for your situation.

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Authoritative Sources

Citations reflect U.S. federal tax law as of the article's last reviewed date.

Related Depreciation and Method Guides

Cost Segregation for Rentals

How a study reclassifies components and what it is worth.

Commercial Real Estate Depreciation

The 39 year baseline and the components that can be accelerated.

Choosing a Cost Seg Provider

Provider models, deliverables, and audit support compared.

Car Wash Cost Segregation

An asset class where a large share of the building qualifies for accelerated treatment.