What Is Form 3115? The IRS Form That Unlocks Catch-Up Depreciation

If you bought a rental property in a prior year and never did a cost segregation study, you haven't missed your chance. Form 3115 (Application for Change in Accounting Method) is the IRS's mechanism for retroactively correcting a suboptimal depreciation method — and the result is a single large deduction in the current year.

Why You Don't Have to Amend Returns

When you bought your rental property, the IRS assigned you a default depreciation method: straight-line over 27.5 years. Cost segregation is a change from that default to accelerated MACRS depreciation for individual components. The IRS treats this as a change in accounting method, not a correction of an error.

Changes in accounting method are handled via Form 3115, not amended returns. The entire cumulative benefit of switching methods — all the depreciation you should have taken in prior years but didn't — flows into your current-year return as a single deduction called the Section 481(a) adjustment.

The Look-Back Study Process

1. Commission a retroactive cost segregation study: An engineer analyzes the property back to its purchase date, reclassifying components and calculating what MACRS depreciation you should have taken each year.
2. Calculate the Section 481(a) adjustment: The engineer computes the difference between depreciation taken (straight-line) and depreciation that should have been taken (MACRS + bonus). This gap is the catch-up amount.
3. Prepare Form 3115: Your CPA completes Form 3115 requesting IRS consent to change accounting method. Most cost segregation changes qualify for automatic consent (no prior IRS approval needed).
4. File with current-year return: Form 3115 attaches to your current-year return; a copy goes directly to the IRS service center. The catch-up deduction appears on Schedule E.
5. Take the deduction: The full Section 481(a) catch-up amount is deductible in the current tax year — even if it represents 5, 10, or more years of missed depreciation.

Is There a Statute of Limitations?

There is no statute of limitations on cost segregation look-back studies. Whether you bought the property 2 years ago or 15 years ago, you can do a retroactive study and file Form 3115 to claim the catch-up. However, practical considerations matter: properties held very long term may have had significant assets already fully depreciated, reducing the catch-up benefit.