To fix depreciation you claimed incorrectly or missed entirely on prior tax returns, a prior depreciation correction almost always runs through IRS Form 3115. That form lets you gather every missed or miscalculated year into one cumulative adjustment on your current return, instead of amending each affected year one at a time. A narrow set of simpler mistakes can be handled with an amended return, but anything that looks like a pattern rather than a slip is treated as a change in accounting method and belongs on Form 3115.
Why the Correction Matters
The tax code reduces an asset’s basis by the depreciation you were entitled to take, not just the depreciation you actually claimed.1Office of the Law Revision Counsel. 26 USC 1016 – Adjustments to Basis The IRS calls these two figures “allowed” (what you deducted) and “allowable” (what the law permitted).
The consequence is blunt. If you owned a rental property for ten years and never claimed a dollar of depreciation, your basis is still treated as though you did. When you sell, your gain is figured from the lower, depreciation-reduced basis, and you owe tax as if you had taken the deductions all along. You lose the benefit without ever having received it. Correcting the record before a sale is often the only way to avoid paying tax on income you never enjoyed.
The rule cuts both ways. Over-depreciate an asset and your basis was reduced too far, which means the IRS can come back for tax on the excess.
Amended Return or Form 3115
The type of error decides the form. A math mistake on a single return — transposed digits, one asset left off the schedule — can be fixed with an amended return. Individuals use Form 1040-X2Internal Revenue Service. About Form 1040-X – Amended U.S. Individual Income Tax Return and corporations use Form 1120-X.3Internal Revenue Service. About Form 1120-X You generally have three years from when the original return was filed, or two years from when you paid the tax, whichever is later.4Office of the Law Revision Counsel. 26 USC 6511 – Limitations on Credit or Refund
Anything more systemic is a change in accounting method and requires Form 3115. The IRS puts the following errors in that bucket:
- Wrong recovery period, such as depreciating 7-year property over 10 years
- Wrong method, such as straight-line where an accelerated method was allowed
- Complete omission — failing to claim any depreciation for two or more consecutive years
- Wrong convention, such as using the half-year convention when the mid-quarter convention was required
The advantage is that Form 3115 reaches errors from years the amended-return window has already closed. You can correct a mistake stretching back a decade or more in a single filing.
Calculating What You Should Have Deducted
Before you can file either form, you need the correct depreciation figure for each affected year. For most tangible property placed in service after 1986, that means running the numbers under MACRS.5Internal Revenue Service. Publication 946 – How To Depreciate Property Three inputs drive the calculation: depreciable basis, recovery period, and convention.
Depreciable basis is generally what you paid, including sales tax, delivery, and installation. Trade-in allowances, insurance reimbursements, and certain credits reduce it.6Internal Revenue Service. Topic No. 703 – Basis of Assets
The recovery period is set by property class. Common ones:
- 5-year: computers, peripheral equipment, automobiles, light trucks
- 7-year: office furniture, desks, safes, most general-purpose machinery
- 15-year: qualified improvement property (interior improvements to nonresidential buildings)
- 27.5-year: residential rental buildings and their structural components7Internal Revenue Service. Publication 527 – Residential Rental Property
- 39-year: nonresidential real property such as office buildings and retail stores
A rental building depreciated over 39 years instead of 27.5 is a classic method-change error, compounding every year it goes uncorrected. Interior improvements to nonresidential buildings depreciated over 39 years instead of 15 as qualified improvement property are another.8Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System Not every interior change qualifies as QIP — enlargements, elevators, escalators, and changes to internal structural framework are excluded, and residential rental buildings don’t qualify at all.
Apply the MACRS percentage tables in Publication 946 to each year the asset was in service. The sum is your allowable prior depreciation. Subtract what you actually claimed, and the difference is what the correction will move.
Filing Form 3115
Most depreciation corrections qualify for the IRS’s automatic consent procedures, so you don’t need advance permission. File in duplicate: attach the original to your timely filed federal income tax return for the year of change, and mail a signed copy to the IRS office in Ogden, Utah.9Internal Revenue Service. Where to File Form 3115
On the form, you describe the property, identify the impermissible method you used and the permissible method required, and compute the cumulative difference. That difference is the Section 481(a) adjustment. Schedule E of Form 3115 is the depreciation-specific schedule and asks for each asset’s description, its placed-in-service year, and the two methods being compared.10Internal Revenue Service. Instructions for Form 3115 – Application for Change in Accounting Method
Timing is strict. The form must be attached to a return filed by its due date including extensions. If you’ve already filed the return for the year and then realize the change is needed, you generally have to wait until the next tax year to make it.
What the Section 481(a) Adjustment Does to Your Tax
The Section 481(a) adjustment is the dollar figure that bridges what you claimed and what you should have claimed across every prior year. Which direction the error ran determines how the tax hits.
If you under-depreciated, the cumulative shortfall is a negative adjustment that reduces your taxable income, and you take the entire amount in the year of change.11Internal Revenue Service. IRM 4.11.6 – Changes in Accounting Methods This is the lump-sum catch-up that makes Form 3115 so useful.
If you over-depreciated, the excess is a positive adjustment that increases your taxable income. The IRS generally lets you spread that increase over four years: the year of change plus the next three. If you’re under examination when the change is made, the spread shortens to two years.10Internal Revenue Service. Instructions for Form 3115 – Application for Change in Accounting Method Either way, you avoid reopening every affected year individually.
Bonus Depreciation and Section 179
Missed bonus depreciation is corrected the same way as any other missed MACRS deduction: the entire shortfall flows through as a negative Section 481(a) adjustment on Form 3115. Under the One Big Beautiful Bill Act signed in July 2025, 100% bonus depreciation applies permanently to qualifying property acquired and placed in service after January 19, 2025. Property placed in service between 2023 and January 19, 2025 falls under the phase-down schedule from the Tax Cuts and Jobs Act (80% for 2023, 60% for 2024).
Section 179 is different, and this is the trap. The election to expense property under Section 179 must be made on the original return for the year the property was placed in service. You cannot make a new Section 179 election on an amended return filed after the due date. The one exception: if you timely filed the original return without making the election, you can still elect Section 179 on an amended return filed within six months of the original due date, not counting extensions.12Internal Revenue Service. Rules for Making a Section 179 Election (INFO 2001-0200) Miss that window and the Section 179 election is gone for that property. You can still claim regular MACRS depreciation going forward, and Form 3115 can catch up on any MACRS depreciation you also missed, but the immediate expensing benefit is lost.
For 2026, the Section 179 maximum is $2,560,000, phasing out dollar-for-dollar once total qualifying property placed in service exceeds $4,090,000. Applying the wrong year’s limit or miscalculating the phase-out may be a math error correctable by amended return, or a method change requiring Form 3115, depending on the pattern.
Fix It Before You Sell
Every dollar of prior depreciation, allowed or allowable, reduces the asset’s basis and increases your taxable gain on sale. For equipment, vehicles, machinery, computers, and furniture — Section 1245 property — the portion of the gain attributable to depreciation is recaptured as ordinary income rather than taxed at capital gains rates.13Office of the Law Revision Counsel. 26 USC 1245 – Gain From Dispositions of Certain Depreciable Property For buildings and structural improvements, the accumulated straight-line depreciation becomes unrecaptured Section 1250 gain, taxed at a maximum federal rate of 25%.
The allowed-or-allowable rule means the recapture applies whether or not you actually took the deductions. A rental owner who never claimed depreciation still owes the 25% recapture tax on the full allowable amount at sale. Filing Form 3115 to catch up before the closing table is often the single most valuable tax move available to a long-term rental owner.
State Returns Don’t Automatically Follow
A federal correction doesn’t fix your state returns on its own. Many states conform to federal depreciation rules, but a significant number decouple from bonus depreciation, Section 179, or both. A large federal catch-up deduction on Form 3115 may not be allowed at the state level, or may require a separate filing. Check your state’s conformity before assuming the federal correction carries through.