Cost segregation studies used to be a tool for big commercial real estate. $5M warehouses, hotels, office buildings. Anything smaller — a duplex, a single-family rental — and the cost of the study ate the benefit.
That changed in 2025. With the OBBBA restoring permanent 100% bonus depreciation, the math now works on much smaller properties than before. A study that was marginal on a $400K residential rental five years ago can produce a clear five-figure first-year tax benefit today.
Here's when the math actually works, what to expect, and the three mistakes that ruin first-time studies.
What Cost Segregation Actually Does
The IRS lets you depreciate residential rental property over 27.5 years (commercial: 39). That's slow. On a $500K building basis, you get ~$18K of depreciation per year.
A cost segregation study takes that same building and breaks it into shorter-lived components:
- 5-year property — appliances, carpet, decorative fixtures, certain trim
- 7-year property — furniture, certain equipment
- 15-year property — land improvements (fencing, paving, landscaping, lighting)
- 27.5- or 39-year property — the building shell
The 5/7/15-year buckets are all bonus-depreciation eligible. With 100% bonus depreciation restored, every dollar reclassified into those buckets becomes a year-one deduction instead of being spread over decades.
On a typical residential rental, a study reclassifies 20-30% of the building basis into bonus-eligible categories.
The Cost of a Study
Cost segregation studies range from:
- Engineered ("full") study — $4,000-$15,000+ depending on property size. Most defensible in audit, most accurate.
- Hybrid / DIY-with-engineer-review — $1,500-$3,500. Less common, decent for smaller properties.
- Cost seg software (recent development) — $500-$1,500 self-service with software like KBKG or DIY Cost Segregator. Use cautiously — quality varies.
For most residential rentals up to ~$2M, an engineered study from a reputable firm runs $3,500-$6,000.
The Sweet Spot for 2026
With OBBBA's 100% bonus depreciation:
| Property Value | Building Basis (~80%) | Reclassified (~25%) | Year-1 Tax Savings (37% marginal) | Study Cost | ROI |
|---|---|---|---|---|---|
| $300K | $240K | $60K | $22,200 | $4,000 | 5.5x |
| $500K | $400K | $100K | $37,000 | $5,000 | 7.4x |
| $1M | $800K | $200K | $74,000 | $7,500 | 9.9x |
| $2M | $1.6M | $400K | $148,000 | $10,000 | 14.8x |
These are rough numbers, but the pattern holds: the math is strongly positive on residential rentals from ~$300K up. Below that, the study cost starts to eat the benefit. Above $1M, it's almost always a clear win.
The Critical Caveat: You Need Income to Offset
A $100K depreciation deduction is only valuable if you have $100K of income to offset against it. Two scenarios:
Scenario A: You qualify as a Real Estate Professional
Depreciation losses become non-passive. They can offset your commission income, your spouse's W-2, anything. Cost seg is wildly valuable. See the REPS post.
Scenario B: You don't qualify as REPS
Depreciation losses stay passive. They can only offset passive income (other rentals, certain partnerships). If you don't have offsetting passive income, the losses suspend forward — they don't disappear, but the benefit defers until you have passive income (often the year you sell the property).
This is the single biggest miss I see. Investors do an expensive cost seg study, generate huge paper losses, and then... can't use them. Always confirm with your CPA that the losses will be deductible this year before paying for the study.
The Three Biggest Mistakes
Mistake 1: Doing the study without REPS or passive income to offset
You spend $5,000 on a study that generates $80K of deductions you can't use until 5 years from now. The math goes negative. Confirm offsetting income first.
Mistake 2: Doing the study on a property you'll sell within a few years
The accelerated depreciation comes with accelerated recapture on sale. You'll recapture the bonus depreciation at ordinary rates (up to 25-37%, not the 15-20% long-term cap gains rate). On a property you'll hold 30 years, this is fine — the deferral is worth it. On a property you'll flip in 4 years, you're often better off without the study.
Mistake 3: Using a cheap study that doesn't survive an audit
The IRS audits cost seg positions, and the difference between a $1,500 software-generated study and a $5,000 engineered study often shows up in an audit. The cheap study can fail to defend the reclassifications, and you lose the deductions plus pay penalties.
If the study is producing $50K+ of first-year deductions, the extra $3,000 for a proper engineered study is cheap insurance.
When to Do the Study
Two timing windows work:
- The year you place the property in service. Best timing — the bonus depreciation lands in the same tax year as the purchase.
- Look-back study on a property you already own. The IRS allows you to "catch up" missed depreciation via Form 3115 (Change in Accounting Method). You can do a cost seg study on a property you bought 3 years ago and claim the catch-up in the current year. This is genuinely powerful for investors who have owned property for a few years without a study.
How to Find a Good Cost Seg Firm
Look for:
- Engineered studies (mention IRS Audit Technique Guide for Cost Segregation)
- Specific real estate experience — residential vs. commercial firms differ
- Site visits or video walk-throughs (not pure desk reviews of photos)
- References from CPAs and investors who've used them
- Audit defense included or available
Common reputable firms in this space include KBKG, Bedford Cost Segregation, MS Consultants, and ETS (Engineered Tax Services). Always get 2-3 quotes — pricing varies more than you'd expect.
The Bigger Point
Cost segregation used to be reserved for big-dollar commercial real estate. With OBBBA's restoration of 100% bonus depreciation in 2025, the math now works on properties as small as $300K — particularly for investors who qualify as Real Estate Professionals.
The savings are real. The execution requires you to actually have offsetting income, a long enough hold period, and a study that will survive an audit. When those three conditions line up, cost seg is among the highest-ROI moves available to a real estate investor in 2026.
This is exactly the kind of move I help coaching clients evaluate — running the actual numbers on your specific property and tax situation, then handing the licensed advice off to your CPA for execution.
About the author: Lance Hulsey is a California real estate broker (DRE# 01724888), former CFO of Room Real Estate (a ~$400M California team), and co-investor in the KW Thrive SC Keller Williams franchise in Capitola, CA. He coaches agents on the financial side of the business through The Agent's CFO.