Cost Segregation After the One Big Beautiful Bill: How 100% Bonus Changes the Math in 2026

I have engineered over 1,000 cost segregation studies across every major property type. I have run the numbers at every bonus depreciation rate from 100% down to 40% and back up again. And I can tell you without hesitation: the One Big Beautiful Bill changed the cost segregation equation more than any single piece of legislation since the TCJA itself.

If you have been on the fence about cost segregation — or if you ran the numbers in 2024 and decided the ROI was not compelling enough — it is time to recalculate. The math has fundamentally shifted, and properties that did not pencil at 40% or 60% bonus now deliver extraordinary returns at 100%.

The Bonus Depreciation Roller Coaster: 2017–2029

To understand why the OBBB matters so much, you need to understand the journey bonus depreciation has taken over the past decade. I have watched this play out in real time — and I have seen how each rate change directly affected whether investors moved forward with cost segregation studies.

The Tax Cuts and Jobs Act of 2017 introduced 100% bonus depreciation, allowing investors to deduct the full cost of qualifying short-life assets in year one. This was transformative for cost segregation. Suddenly, a study that reclassified 24% of a building's basis did not just accelerate depreciation — it front-loaded the entire deduction into a single tax year.

But the TCJA included a built-in phase-down schedule. Starting in 2023, bonus depreciation began declining by 20 percentage points per year:

The OBBB, signed into law on July 4, 2025, did not just stop the phase-down — it reversed it entirely. The bill retroactively restored 100% bonus depreciation for property placed in service after January 19, 2025, and extends it through December 31, 2029. For a complete breakdown of every provision, see our One Big Beautiful Bill Complete Guide.

Related: One Big Beautiful Bill Act: 100% Bonus Depreciation Made Permanent (Overline)

The Math: Same Property, Four Different Bonus Rates

This is where the OBBB's impact becomes visceral. I am going to use a single property — a $500,000 single-family rental — and show you how the same cost segregation study produces dramatically different results depending on the bonus depreciation rate in effect.

Look at that progression. The same property, the same engineering analysis, the same $1,800 study fee — but the ROI swings from 7.9x to 19.7x depending entirely on the bonus depreciation rate. At 100% bonus, every dollar you spend on the study returns nearly twenty dollars in first-year tax savings.

For a deeper dive into how these savings are calculated and what drives reclassification percentages, see our 2026 Pricing Transparency Report and the benchmark data from 8,000+ studies.

Why 100% Bonus Makes Cost Seg Viable for Smaller Properties

This is the part of the OBBB story that does not get enough attention. During the phase-down, I watched investors with $250,000–$400,000 properties run the numbers and conclude that cost segregation was not worth it. At 40% bonus, a $300,000 property might generate $8,000–$10,000 in first-year savings against a $1,800 study cost. That is a 4.4–5.6x ROI — still positive, but not compelling enough for many investors to act.

At 100% bonus, that same $300,000 property generates $20,000–$26,000 in first-year savings. The ROI jumps to 11–14x. That is the difference between "I will think about it" and "let us start today."

At 40% bonus, I generally told investors that cost segregation started making clear financial sense around the $350,000–$400,000 range for single-family rentals. Below that, the ROI was positive but modest. At 100% bonus, that threshold drops to roughly $150,000–$200,000. This opens cost segregation to a massive segment of the investor market that was previously priced out — not by the study cost, but by the reduced tax benefit.

As I wrote in our guide to affordable cost segregation, the combination of flat-fee pricing ($1,800 for SFH) and 100% bonus depreciation means cost segregation is now viable for the majority of rental property investors, not just those with high-value portfolios.

Retroactive Application: Filing Amended Returns and Form 3115

The OBBB's retroactive effective date — January 20, 2025 — creates a unique opportunity for investors who acquired property in 2025 and already filed their tax returns using the old 40% bonus rate. You have two paths to capture the additional benefit:

Path 1: Amended Return (Form 1040-X)

If you filed your 2025 return using 40% bonus depreciation and placed property in service after January 19, 2025, you can file an amended return to claim the full 100% bonus. This is straightforward — your CPA recalculates the depreciation deduction using the higher rate and files the amendment.

Path 2: Form 3115 (Change in Accounting Method)

For investors who placed property in service before 2025 and filed cost segregation studies during the phase-down period, Form 3115 is the mechanism to claim catch-up depreciation. This is particularly relevant if you:

• Completed a cost segregation study in 2023 at 80% bonus
• Completed a study in 2024 at 60% bonus
• Own property that was placed in service during 2025 before the OBBB passed

The 3115 filing allows you to take a "catch-up" adjustment — a Section 481(a) adjustment — that captures the cumulative difference between what you claimed and what you were entitled to under 100% bonus. This adjustment is taken entirely in the year of change, creating a potentially large one-time deduction.

For the complete step-by-step action plan on how to take advantage of the OBBB, including filing timelines and CPA coordination, see our One Big Beautiful Bill Action Plan.

Impact by Property Type: Where the Gains Are Largest

The OBBB does not affect all property types equally. Properties with higher reclassification rates see proportionally larger benefits from the return to 100% bonus. Based on our data from 1,000+ completed studies and 8,000+ benchmark studies, here is how the bonus restoration plays out across asset classes:

The percentage increase is always 150% (the mathematical relationship between 40% and 100% of any base number). But the absolute dollar difference varies significantly. A retail property with 32% reclassification sees an additional $28,416 in first-year savings compared to the 40% bonus rate. For investors with short-term rentals, the combination of higher reclassification rates and the material participation loophole makes this particularly powerful.

What This Means for Investors Who Waited

I spoke with hundreds of investors during 2024 and early 2025 who decided to wait on cost segregation. Their reasoning was sound at the time: "If bonus is only 40%, maybe I should wait and see if Congress restores it." Those investors were right to wait — and now it is time to act.

If you own property that was placed in service at any point and you have never done a cost segregation study, the current environment is the best it has been since 2022. You get:

• 100% bonus depreciation — full first-year deduction of all reclassified assets
• Look-back capability — you can study properties acquired years ago and claim catch-up depreciation via Form 3115
• Lower study costs — AI-native platforms like ours deliver engineering-quality studies at $1,800 for SFH, a fraction of traditional firm pricing
• Five-year window — the 100% rate extends through 2029, giving you time to plan but also creating urgency to capture maximum benefit

For a detailed analysis of when cost segregation makes sense and when it does not, see our guide to when cost seg does not make sense. The threshold has shifted dramatically — properties that did not qualify before the OBBB may now deliver strong ROI.

Your 2026 Action Plan

Based on the restored 100% bonus depreciation, here is what I recommend for different investor profiles:

If You Have Never Done a Cost Segregation Study

1. Screen your property. Run it through our free cost segregation calculator. At 100% bonus, any property with a depreciable basis above $150,000 is likely to show strong ROI.
2. Order a study. At $1,800 for SFH, the barrier to entry has never been lower. See our pricing guide for all property types.
3. File a 3115. Your CPA files Form 3115 with your current-year return to claim catch-up depreciation for all prior years. This is a one-time adjustment — no amended returns needed.

If You Did a Study During the Phase-Down (2023–2025)

1. Review your original study. The asset classifications are still valid — nothing needs to be re-engineered.
2. Calculate the differential. Determine how much additional depreciation you are entitled to at 100% versus the rate you originally claimed.
3. File an amended return or 3115. Capture the catch-up adjustment. For 2025 returns filed at 40%, the differential on a $500K property is approximately $21,312 in additional first-year savings.

If You Are Acquiring Property in 2026

1. Order the study at closing. The optimal time is within the first year of ownership. See our timing strategy guide.
2. Factor cost seg into your underwriting. At 100% bonus, the first-year tax savings from cost segregation should be part of your acquisition analysis, not an afterthought.
3. Coordinate with your CPA before year-end. Ensure the depreciation deduction is properly reflected on your return.