You bought a rental property three, five, or even ten years ago and never performed a cost segregation study. Every year since then, you have been depreciating the entire building over 27.5 or 39 years using straight-line depreciation. You left thousands of dollars in accelerated depreciation on the table, year after year.
The good news: you can claim all of that missed depreciation in a single tax year, without amending a single prior return. The mechanism is IRS Form 3115 (Application for Change in Accounting Method), combined with a Section 481(a) adjustment. This is one of the most powerful, underused tools in real estate tax planning.
What Is Form 3115?
Form 3115 is the IRS form used to request a change in your accounting method for a specific item. In the context of cost segregation, it is used to change how you classify and depreciate the components of your rental property. Instead of treating the entire building as a single 27.5-year (residential) or 39-year (nonresidential) asset, you reclassify components into their proper asset classes under IRC Sec. 1245 and IRC Sec. 1250:
- 5-year property: Appliances, carpeting, vinyl flooring, cabinetry, certain electrical and plumbing components
- 7-year property: Furniture, office equipment, certain fixtures and finishes
- 15-year property: Land improvements including driveways, sidewalks, landscaping, fencing, parking areas, and exterior lighting
- 27.5 or 39-year property: The remaining structural components of the building
This reclassification is not a special election or a loophole. It reflects the correct depreciation treatment under the Internal Revenue Code. Form 3115 simply corrects the method you have been using to match what the tax code actually requires.
The Section 481(a) Adjustment: Your Catch-Up Mechanism
The real power of Form 3115 is the Section 481(a) adjustment. This is the calculation that captures all the depreciation you missed from the date the property was placed in service through the beginning of the year of change.
Here is how it works:
- Step 1: Perform a cost segregation study on the property, identifying all components and their proper asset classes and recovery periods.
- Step 2: Calculate the total depreciation you should have claimed under the new method (accelerated depreciation for the reclassified components, including bonus depreciation if the property was eligible in the year placed in service) from the placed-in-service date through the beginning of the year of change.
- Step 3: Calculate the total depreciation you actually claimed under the old method (straight-line over 27.5 or 39 years) during the same period.
- Step 4: The difference is your Section 481(a) adjustment. If you under-depreciated (which is almost always the case with a cost seg catch-up), the adjustment is negative, meaning it is a deduction.
- Step 5: Claim the entire negative 481(a) adjustment as a deduction on your current-year tax return. No amended returns needed.
A negative Section 481(a) adjustment (favorable to the taxpayer) is taken in full in the year of change. A positive adjustment (unfavorable) is spread over four years. For cost segregation catch-ups, the adjustment is virtually always negative.
Real Example: Property Purchased in 2020, Cost Seg in 2026
Consider an investor who purchased a long-term rental property in 2020 for $400,000. After subtracting $60,000 for land, the depreciable basis is $340,000. The investor has been depreciating the entire $340,000 over 27.5 years using straight-line depreciation.
What the Investor Actually Claimed (2020 through 2025)
| Year | Straight-Line Depreciation Claimed |
|---|---|
| 2020 (partial year, placed in service July) | $5,669 |
| 2021 | $12,364 |
| 2022 | $12,364 |
| 2023 | $12,364 |
| 2024 | $12,364 |
| 2025 | $12,364 |
| Total Claimed (Old Method) | $67,489 |
What the Investor Should Have Claimed (Cost Seg Method)
A cost segregation study identifies the following reclassifications:
- 5-year property: $51,000 (15% of depreciable basis)
- 7-year property: $34,000 (10% of depreciable basis)
- 15-year property: $34,000 (10% of depreciable basis)
- 27.5-year structural: $221,000 (65% of depreciable basis)
In 2020, the property was placed in service when 100% bonus depreciation was still in effect under the TCJA. Under the correct method, the investor should have claimed:
- 100% bonus on 5-year property: $51,000
- 100% bonus on 7-year property: $34,000
- 100% bonus on 15-year property: $34,000
- Straight-line on 27.5-year structure (partial year 2020 through 2025): approximately $43,866
Total depreciation that should have been claimed: $162,866
The 481(a) Adjustment
| Calculation | Amount |
|---|---|
| Depreciation under new method (should have claimed) | $162,866 |
| Depreciation under old method (actually claimed) | $67,489 |
| Section 481(a) Adjustment (deduction) | ($95,377) |
The investor claims a $95,377 deduction on their 2026 tax return. At a 37% marginal rate, that is $35,289 in federal tax savings, all in one year, without amending a single prior return.
If this investor also operates a short-term rental and materially participates, that $95,377 deduction is non-passive and offsets W-2 income directly.
The Automatic Consent Procedure
One of the most common concerns investors have about Form 3115 is whether they need IRS approval. For cost segregation changes, the answer is no.
Rev. Proc. 2015-13 (as modified by Rev. Proc. 2015-14, Rev. Proc. 2019-43, and subsequent guidance) established an automatic consent procedure for certain accounting method changes, including changes in depreciation method, recovery period, and convention. Cost segregation reclassifications fall squarely within the automatic consent framework.
Under automatic consent:
- You do not need to request a private letter ruling from the IRS
- You do not need advance approval
- You file Form 3115 with your current-year tax return (the "year of change")
- You mail a duplicate copy to the IRS National Office in Ogden, Utah
- The change is effective for the year of change and all subsequent years
The designated change number (DCN) for depreciation method changes is typically DCN 7 (change in depreciation method, useful life, or convention for depreciable assets). Your tax advisor will identify the correct DCN for your specific situation.
Filing Requirements
To properly file Form 3115 for a cost segregation catch-up:
- Complete the cost segregation study. You need a qualified study that identifies each component, its proper asset class, recovery period, and depreciable amount. This study supports the reclassification and is your documentation in case of an IRS inquiry.
- Calculate the Section 481(a) adjustment. Compare depreciation under the old method versus the new method from the placed-in-service date through the beginning of the year of change.
- Complete Form 3115. Include all required schedules, the 481(a) adjustment calculation, and the designated change number.
- Attach Form 3115 to your timely filed tax return (including extensions) for the year of change.
- Send a duplicate copy to the IRS National Office at the address specified in the current Revenue Procedure (currently the Ogden, UT campus).
The form must be filed with the original, timely filed return. If you miss the filing deadline (including extensions), you cannot file Form 3115 for that year of change and must wait until the next tax year.
Statute of Limitations Considerations
A common question: "What about the statute of limitations on those earlier years?"
The Section 481(a) adjustment is not an amendment of prior returns. It is a current-year adjustment that captures the cumulative effect of the accounting method change. The statute of limitations on prior years is irrelevant because you are not reopening those returns. You are simply computing the correct depreciation as of the beginning of the year of change and claiming the difference on the current return.
This is one of the key advantages of Form 3115 over amending prior returns. Even if the statute has run on your 2020 and 2021 returns, you still capture the depreciation from those years through the 481(a) adjustment on your 2026 return.
Why Catch-Up Can Be MORE Valuable Than Doing Cost Seg at Purchase
This may seem counterintuitive, but there are scenarios where performing a cost segregation study years after purchase and filing Form 3115 creates a larger one-time deduction than doing the study at closing:
- Multiple years of missed depreciation in one lump sum. If you bought in 2020 and do cost seg in 2026, you capture six years of missed accelerated depreciation in a single tax year. A study done at closing in 2020 would have spread bonus depreciation across Year 1 only (with the structure continuing on straight-line). The catch-up combines the bonus depreciation benefit with years of additional straight-line difference.
- Higher income year. If your income is higher in 2026 than it was in 2020, the deduction is worth more at your current marginal rate.
- Strategic timing. You can choose which tax year to file the Form 3115, allowing you to place the deduction in the year where it provides the most value.
Of course, doing cost seg at purchase is still the ideal approach because you get the time value of the deductions earlier. But if you missed that window, Form 3115 ensures you are not penalized for waiting.
Common Mistakes When Filing Form 3115
Form 3115 is a powerful tool, but the filing requirements are precise. Common mistakes include:
- Missing the filing deadline. The form must be attached to a timely filed return (including extensions). Filing late means you wait another year.
- Failing to send the duplicate copy. The IRS requires a copy mailed to the National Office. Skipping this step can invalidate the filing.
- Using the wrong designated change number (DCN). Each type of accounting method change has a specific DCN. Using the wrong one causes processing delays or rejection.
- Incorrect 481(a) calculation. Errors in calculating what you should have claimed versus what you actually claimed produce an incorrect adjustment. This invites IRS scrutiny.
- No supporting cost segregation study. The reclassification must be supported by a qualified engineering-based cost segregation study. Without it, the IRS can challenge every component classification.
- Filing during an audit year. Under certain circumstances, automatic consent is not available for a year under examination. Your tax advisor should verify eligibility before filing.
- Inconsistent treatment across properties. If you own multiple properties and file Form 3115 for one, make sure your depreciation treatment is consistent across your portfolio or file separate changes as needed.
Form 3115 for STR and LTR Properties
The Form 3115 catch-up works for both short-term and long-term rental properties. The key difference is in how the resulting deduction is treated:
- STR with material participation: The 481(a) adjustment flows through as a non-passive deduction, offsetting W-2 and active income. This makes the catch-up especially valuable for STR owners who have been leaving non-passive deductions unclaimed for years.
- LTR (passive): The 481(a) adjustment is a passive deduction. It offsets passive income or carries forward as a passive loss. Still valuable, but the timing of the benefit depends on your passive income situation.
For investors considering converting an LTR to an STR, performing the cost seg study and filing Form 3115 in the same year you convert can create a powerful one-two combination: the reclassification captures missed depreciation, and the STR treatment makes the deduction non-passive going forward.
AE Tax Advisors Pricing and Process
At AE Tax Advisors, we handle the entire Form 3115 process from start to finish. Our team performs the cost segregation study, calculates the Section 481(a) adjustment, prepares the Form 3115, and ensures the duplicate copy is filed with the IRS National Office.
- Full tax advisory engagement: $7,800, covering cost segregation, entity structuring, deduction optimization, and ongoing tax planning
- Amendment work (prior-year corrections): $2,500 per year
- Cost segregation studies: Available as part of our advisory engagement or on a standalone basis
We work exclusively with real estate investors and business owners. If you own property that has been depreciating on straight-line for years, the catch-up deduction is almost certainly larger than you expect. Use our cost segregation calculator to run a quick estimate, then book your free assessment to see the exact numbers for your portfolio.
Key Takeaways
- Form 3115 lets you claim all missed accelerated depreciation in a single tax year through a Section 481(a) adjustment.
- No amended returns are needed. The entire catch-up deduction goes on your current-year return.
- The change falls under automatic consent procedures (Rev. Proc. 2015-13, as modified). No IRS permission required.
- The statute of limitations on prior years does not matter because you are not reopening old returns.
- The catch-up can sometimes be MORE valuable than doing cost seg at purchase, because you capture multiple years of missed depreciation at once.
- Both STR and LTR properties qualify, but STR owners with material participation get non-passive treatment on the deduction.
- Filing must be done correctly: attach to a timely filed return, send duplicate to the IRS National Office, use the correct DCN.