A Form 3115 depreciation example works like this: you rebuild the depreciation schedule for the asset under the correct method from its placed-in-service date, compare that total to what you actually deducted, and the difference becomes a single Section 481(a) catch-up adjustment on your current return. A negative number (you under-depreciated) is deducted in full in the year of change. A positive number (you over-depreciated) is spread across four years, starting with the year of change.
What You Need Before You Do the Math
The year of change is the tax year you’re requesting the new method for. Your 481(a) calculation runs from the asset’s placed-in-service date through the last day of the tax year immediately before the year of change.1
For every asset in the change, pull together:
- The placed-in-service date, which anchors both the old and new schedules.
- The original cost basis, including capitalized costs such as sales tax or installation.
- The method, recovery period, and convention you actually used, plus depreciation claimed each year.
- The correct method, recovery period, convention, and system (GDS or ADS).
Build a side-by-side schedule of what you deducted against what you should have deducted. The cumulative difference is the 481(a) number.
The Section 481(a) Formula
The adjustment prevents deductions from being duplicated or skipped when you switch methods. It captures the entire cumulative difference from the placed-in-service date through the beginning of the year of change, in a single figure.
Total depreciation that should have been taken under the correct method, minus total depreciation actually taken under the incorrect method. The sign tells you what happens next:
- Negative adjustment: you under-deducted. The full amount is an additional deduction in the year of change.
- Positive adjustment: you over-deducted. The amount is spread over four tax years — one quarter in the year of change and one quarter in each of the next three.
That one-year-versus-four-year split is the practical stakes of the sign. A negative adjustment lands entirely on the current return. A positive adjustment softens the income pickup by stretching it out.
A Worked Example
You bought machinery for $100,000 on January 1, 2022. You depreciated it on a 5-year straight-line schedule and claimed $20,000 in 2022 and $20,000 in 2023, for $40,000 total. The correct treatment is 7-year MACRS GDS with a half-year convention. You’re filing Form 3115 with your 2024 return, so 2024 is the year of change and the 481(a) calculation covers 2022 and 2023.
Under 7-year MACRS, the first-year rate is 14.29% and the second-year rate is 24.49%. On $100,000, that’s $14,290 for 2022 and $24,490 for 2023, or $38,780 total under the correct method.
Now the subtraction: $38,780 (should have taken) minus $40,000 (actually took) equals negative $1,220. The sign is negative, so the entire $1,220 is deducted on your 2024 return. From 2024 forward, depreciation uses the correct 7-year MACRS rates applied to the original $100,000 basis.
If the Adjustment Had Been Positive
Flip the facts so that you under-depreciated under the old method and the calculation produces, say, a positive $12,000 adjustment. Instead of a single hit, that $12,000 is picked up as $3,000 of additional taxable income in the year of change and $3,000 in each of the three following tax years.
Where the Numbers Go
The 481(a) adjustment amount, marked positive or negative, goes on Part IV, Line 25 of Form 3115. The asset-by-asset calculation that supports it is documented on Schedule E. You’ll also enter the Designated Change Number that identifies the change you’re making. For a switch from an impermissible to a permissible depreciation method — the most common depreciation correction — that’s DCN 7.
The adjustment then carries to your regular return as “other income” or “other deduction,” labeled as a Section 481(a) adjustment. Which return depends on the entity: Schedule C of Form 1040, Form 1065, Form 1120, or whichever return applies to your business.
Two Copies, Two Places
Automatic depreciation changes are filed in two places. The original Form 3115 goes with your timely filed federal return for the year of change. A duplicate signed copy is separately mailed to the IRS in Ogden, Utah, on or before the date your return is filed. The address for automatic changes is Internal Revenue Service, Ogden, UT 84201, Attn: M/S 6111.
If your return is late, or the duplicate copy arrives after your return filing date, the IRS can treat the request as invalid. If you’re on extension, the Form 3115 deadline tracks the extended due date as long as the return is actually filed by then.
When Form 3115 Isn’t the Right Fix
Not every depreciation mistake is a method change. A math mistake, a transposition, or a wrong number plugged into an otherwise correct formula is a simple error — fix it by amending the affected return or correcting the current year’s Form 4562. Form 3115 is for method changes, and the IRS treats a depreciation practice as an adopted method once you’ve used it the same way on two or more consecutively filed returns. That’s the two-year rule: if the incorrect treatment appeared on only one return, amend that return instead. If it appeared on two or more, use Form 3115.
The kinds of depreciation problems that do call for Form 3115 include using the wrong recovery period (5 years when MACRS requires 7, or vice versa), using straight-line where the 200% declining balance method under GDS is required, using GDS when ADS is mandatory (for example, certain listed property or property used outside the United States), and failing to depreciate an asset at all for two or more years and now starting.
Most depreciation corrections qualify for the IRS’s automatic change procedures, which means no advance approval and no user fee — you file the form correctly and consent is considered granted. Non-automatic changes go to the IRS National Office with a user fee and require a letter ruling, and are typically reserved for changes not listed in the automatic procedures or for taxpayers under examination for the item they want to change.