Cost Seg in Year of Purchase vs Look-Back Study: Which Wins?
Cost segregation in the year of purchase captures 100% bonus depreciation under OBBBA for post-Jan-19-2025 acquisitions, producing the largest first-year deduction. Look-back studies via Form 3115 with Designated Change Number 7 under Rev. Proc. 2022-14 catch up missed depreciation from prior years in a single Section 481(a) adjustment. For property already owned, look-back is the only path. For property being acquired, year-of-purchase produces a larger nominal benefit but look-back can be more time-flexible.
Year-of-purchase mechanics
Cost segregation in the acquisition year applies the bonus depreciation rate that corresponds to the binding contract date. Post-Jan-19-2025 binding contracts qualify for 100% bonus depreciation under amended Section 168(k) per Public Law 119-21 (OBBBA). The reclassified portion of basis deducts entirely in year one.
The engineering work happens after closing. WeCostSeg typically begins the preliminary analysis within a week of closing and delivers the final engineer-signed report within 2 to 3 weeks for residential or 3 to 4 weeks for commercial. The deduction lands on the year-of-acquisition tax return.
Look-back study mechanics
A look-back cost segregation study captures missed depreciation from prior years via Form 3115 (Application for Change in Accounting Method) under Designated Change Number 7 in Rev. Proc. 2022-14. The Section 481(a) adjustment computes the difference between depreciation that would have been taken under the corrected method versus what was actually taken, and posts that difference as a deduction in the year of change.
No amended returns are required. The form is filed in duplicate: the original attaches to the timely-filed return for the year of change, and a signed duplicate is mailed to the IRS Ogden, Utah service center under Rev. Proc. 2015-13. WeCostSeg includes Form 3115 preparation at no extra cost when bundled with a look-back study.
Which produces the larger deduction
For acquisitions on or after January 20, 2025, year-of-purchase produces the larger nominal benefit because 100% bonus applies. A $1M residential rental yields roughly $280K of first-year deduction under year-of-purchase cost seg.
Look-back on a property acquired in 2021 (when 100% bonus applied under TCJA) produces a similar nominal benefit, just deferred. The Section 481(a) catch-up captures roughly $200K to $300K on a $1M property owned 5 years without cost seg, delivered in the year of change.
| Path | Year-one deduction | Tax savings at 32% | Caveat |
|---|---|---|---|
| Year-of-purchase (post-Jan-19-2025) | $280K | $90K | Must own the property, engagement same year |
| Look-back via Form 3115 (acquired 2021) | $170K to $250K catch-up | $54K to $80K | Must still own, Section 481(a) timing |
| Year-of-purchase (pre-Jan-20-2025 binding) | $112K to $150K | $36K to $48K | 40% bonus phase-down rate locked |
When look-back is the only option
Property already owned for one or more tax years where cost segregation was not performed at acquisition. The two-year minimum holding period under DCN 7 means properties placed in service in 2024 or earlier qualify for a 2026 Form 3115 filing.
Look-back is also the right path when the year-of-acquisition tax return was filed without cost seg. The form must accompany the timely-filed return for the year of change. If that year has already been filed, the change is for the next year, not the current year.
Frequently asked questions
- How does WeCostSeg coordinate with my CPA?
- Every engagement follows the three-touch CPA Coordination Protocol. We send a preliminary analysis to your CPA on intake, share the draft report five business days before final delivery, and coordinate Form 3115 filing timing when a Section 481(a) adjustment applies. Your CPA never pays a fee.
- Does this analysis assume 100% bonus depreciation under OBBBA?
- Yes for property acquired with a binding contract on or after January 20, 2025 under Public Law 119-21. Property under a binding contract on or before January 19, 2025 stays on the legacy phase-down: 40% bonus in 2025, 20% in 2026, 0% in 2027 and after.
- Is the five-year audit defense included?
- Yes. Every WeCostSeg engagement includes five years of written audit defense at no extra cost. The defense aligns to the 13 Principal Elements of a Quality Cost Segregation Study under IRS Publication 5653 Chapter 4.
- Can I get a free preliminary analysis?
- Yes. Submit your property details via the free proposal form or WhatsApp. Our engineer returns a written estimate of your first-year deduction within four business hours during US Eastern hours. No payment, no contract.
- Can I do a look-back on a property I bought 10 years ago?
- Yes. There is no statutory deadline. The Section 481(a) catch-up can be claimed in any year the property is still being depreciated and still owned. The earlier you correct, the larger the catch-up because more depreciation has been understated.
Zawwad Ul Sami, Founder
Zawwad Ul Sami is the founder of WeCostSeg, a founder-led cost segregation firm serving real estate investors across the US. He focuses on strategy, pricing, and the firm's overall direction.