Missed Depreciation on Your Rental? Form 3115 Fixes Years at Once
Bought in 2020 and never did the cost seg? Depreciated the wrong schedule since day one? The accounting-method rules are surprisingly generous about cleaning it up.
A guide by Taxstra Tax & Accounting · CPA-led tax strategy for business owners
Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last updated August 19, 2026.
The short answer
You do not amend old returns to fix depreciation; you file Form 3115 with the current one. The change from a wrong (or missing) depreciation method to the right one comes with a Section 481(a) catch-up: every dollar you under-deducted since the property went into service lands as one deduction in the current year, under automatic consent procedures. This is how a look-back cost segregation on a 2020 building produces a five- or six-figure deduction on this year's return, and how never-depreciated rentals escape the trap of paying recapture on deductions they never took.
The three fact patterns this fixes
| Situation | The fix | What lands on this year's return |
|---|---|---|
| Straight-line since purchase; cost seg never done | Look-back study + Form 3115 | Catch-up equal to all the accelerated depreciation the study would have front-loaded |
| No depreciation claimed at all (2+ years) | Form 3115 method change | Every missed year's depreciation, at once |
| Wrong life or method (e.g., 39-yr on residential, land value never split) | Form 3115 correction | The cumulative under-depreciation as a 481(a) adjustment |
| One single year missed or miscomputed | Amend that year instead | A method requires consistency; one year is an error, not a method |
| Schedule from an old cost seg does not tie to the returns | Reconciliation, then 3115 or amendment as facts dictate | Cleanup before it compounds; common in inherited files |
The never-depreciated case deserves the loudest alarm because of the "allowed or allowable" rule: your basis shrinks by the depreciation you were entitled to whether or not you claimed it, so skipping depreciation buys you nothing at sale, you pay recapture math on phantom deductions. Owners who avoided depreciation "to keep it simple" are the single most underserved cleanup group we see, and the 3115 catch-up is pure recovered money for them.
A look-back, worked end to end
2020 short-term rental, $850K basis, straight-line ever since (illustrative)
- Depreciation actually taken (straight-line, ~6 years)
- about $185,000
- Look-back cost seg: 27% reclassified to 5/7/15-year property as of 2020
- about $230,000 of components
- Depreciation that SHOULD have been taken by now (with bonus rules as of 2020 in-service date)
- about $420,000
- Section 481(a) catch-up on this year's return
- about $235,000 deduction
- Tax value at a 37% marginal picture, IF the loss is usable
- roughly $87,000
One filing season, no amended returns. The italicized IF is the real analysis: the catch-up lands as depreciation from the activity, so the passive loss rules decide whether it offsets W-2 income this year (STR material participation or REPS) or joins the suspended pile. Illustrative numbers; the study and the 481(a) computation drive the real ones.
The catch-up obeys every loss limitation
Since the sequencing question decides most of the value, here is the decision frame we actually use with multi-property clients. Rank each property by three numbers: the projected 481(a) adjustment (bigger basis and longer straight-line history mean bigger catch-ups), the usability of the deduction in each candidate year (is there a qualifying STR year, a REPS year, a big gain, or passive income to meet it?), and the expected remaining hold (catch-ups on properties you will sell within a couple of years mostly just prepay their own recapture unless an exchange or step-up is coming). Then assign one catch-up per high-usability year rather than bunching. A household with a REPS year planned next year and a practice-sale gain the year after has two perfect landing zones; filing all three studies this year into a passive pile would have wasted both.
One more planning note that surprises people: the catch-up year is your choice. Unlike the original depreciation, which belonged to specific past years, the 481(a) adjustment lands wherever you file the change. That makes missed depreciation one of the few genuinely portable deductions in the code, and treating it as an asset to be deployed, rather than a mistake to be confessed, is the whole reframe this page exists to make.
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Frequently Asked Questions
Can I do a cost segregation study on a property I bought years ago?
Yes. A look-back study reclassifies the building components as of the original placed-in-service date, and Form 3115 (a change in accounting method) lets you claim ALL the depreciation you should have taken, in one catch-up deduction on the current return. No amended returns, no reopening old years.
What is a Section 481(a) adjustment?
The one-time catch-up that reconciles what you actually deducted with what the new method says you should have deducted since day one. For a look-back cost seg, that difference is typically a large negative adjustment, an extra deduction, taken entirely in the year of change for taxpayer-favorable adjustments.
Do I need IRS permission to make this change?
Depreciation corrections of this kind generally qualify for automatic consent: you file Form 3115 with the current-year return (plus a copy to the IRS), following the current automatic change procedures, and no advance approval or user fee is required. Automatic does not mean casual; the form, the computation, and the study behind it need to be done properly.
I never claimed depreciation at all on my rental. Does this fix that too?
Yes, and it matters more than people realize: when you sell, recapture is computed on depreciation "allowed or allowable," meaning you pay recapture on deductions you never took. Two or more years of missed depreciation is an accounting method that Form 3115 can correct with a full catch-up; a single missed year is generally fixed by amending instead.
When is the look-back study NOT worth it?
When the remaining ownership window is short (you repay the benefit through recapture at sale soon anyway, unless a 1031 or step-up is planned), when the passive loss rules would strand the deduction (no STR/REPS/passive income to absorb it), when the excess business loss cap defers most of it, or when the property is small enough that study plus preparation fees eat the benefit. It is a model, not a reflex.
Does filing Form 3115 increase my audit risk?
The automatic-change procedures exist precisely so routine depreciation corrections happen without examination; you are using the system as designed, with computations attached. What draws scrutiny is not the form but sloppy execution: a 481(a) number with no engineering study behind it, or a change filed for a property whose facts do not support the reclassification. A properly supported 3115 is among the most routine filings in real estate tax.
Can I file the catch-up for a property I already sold?
Generally no; the method change belongs to a year you still hold the property, and the disposition itself trues up depreciation through the gain computation under the allowed-or-allowable rule. If you sold last year having never depreciated properly, the fix runs through the sale-year reporting, sometimes by amendment, and the sooner it is reviewed the more options remain open.
What actually gets filed, and when?
Two copies of Form 3115: one attached to your timely filed return (extensions count) for the year of change, and a duplicate sent to the IRS separately, with the 481(a) computation and the supporting study in your files. There is no user fee for automatic changes. The practical timeline: engage the study early enough that the engineering, the computation, and the return preparation are not all colliding in the first week of April.
Related Questions
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This page is educational, not individualized tax advice. Outcomes depend on your specific facts and documentation. Savings vary by client and results are not typical of every situation. Consult a qualified tax professional before acting on anything here.