100% Bonus Depreciation Is Permanent Now. Here's How to Use Cost Segregation to Eliminate $111,000 in Taxes on a $1 Million Deal.

The Tax Code Changed. Your Depreciation Strategy Didn't.

On July 4, 2025, President Trump signed the One Big Beautiful Bill Act (OBBBA) into law. Buried inside it was one of the most significant tax gifts ever handed to real estate investors: 100% bonus depreciation made permanent, retroactive to January 19, 2025. This wasn't a patch or an extension — it permanently reversed a scheduled phasedown that would have eliminated the deduction entirely by 2027.

Most investors know the bill passed. What far fewer have done is actually act on it.

We are now in June 2026 — halfway through the tax year — and thousands of real estate investors who acquired properties in 2025 or early 2026 are still depreciating those buildings on the standard 27.5-year schedule. That means they're sitting on $30,000 to $250,000 in unclaimed year-one deductions, depending on deal size.

Cost segregation is the mechanism that unlocks bonus depreciation. And in the current tax environment, not running a cost segregation study on a new acquisition is one of the most expensive passive mistakes a real estate investor can make. Here's exactly how to fix that.

What Cost Segregation Actually Is — And Why It's More Powerful Than Ever

A cost segregation study is an engineering-based tax analysis that disaggregates a building's components from the standard 27.5-year (residential) or 39-year (commercial) depreciation schedule into shorter-lived asset categories:

• 5-year property: Appliances, carpeting, specialty lighting, certain electrical components
• 7-year property: Office furniture, equipment built into the structure
• 15-year property: Land improvements — parking lots, sidewalks, fencing, landscaping, exterior signage

Under the old tax code, accelerating depreciation on these categories just meant a faster write-off schedule — the same total deduction spread over fewer years. Under the OBBBA, those reclassified components now qualify for 100% bonus depreciation, meaning you deduct the entire amount in year one. Not over five years. Not over fifteen. Year one.

On a $1 million residential rental property, a typical cost segregation study reclassifies $250,000–$350,000 of the purchase price into these shorter-lived categories. With 100% bonus depreciation, that entire $300,000 hits your tax return as a single-year deduction. At the 37% marginal rate, you just created $111,000 in federal tax savings. The study itself costs $2,500–$4,000.

That's a 27x to 44x return on the cost of the study. On a single deal.

The OBBBA stacked additional advantages on top of this core provision:

• The 20% Qualified Business Income (QBI) deduction is now permanent — landlords operating through LLCs or S-corps can continue stacking this deduction on top of depreciation losses indefinitely
• The federal estate exemption is permanent at $15 million per person ($30M married) — critical for investors building multi-generational portfolios
• 1031 exchanges remain fully intact with no dollar caps or restrictions added
• The SALT deduction cap rose from $10,000 to $40,000 for 2025–2029 (note: this only affects personal property taxes on Schedule A — rental property taxes on Schedule E were always fully deductible)

The combination of permanent 100% bonus depreciation and permanent QBI deduction is why serious real estate tax planners are calling 2026 the best tax year for real estate investors in a generation.

The Numbers

According to data compiled by TheRealEstateCPA.com in 2026, cost segregation studies on properties between $500,000 and $2,000,000 typically reclassify 28–32% of the purchase price into accelerated categories. On multifamily deals, that number runs higher — 30–40% is common due to more reclassifiable personal property and land improvements.

Here's what the math looks like at different property sizes, assuming a 37% marginal tax bracket and a $3,000 study cost:

The look-back opportunity — this is the one most investors are sleeping on: If you bought properties before 2025 and never commissioned a cost segregation study, you can still capture missed depreciation retroactively — without amending prior returns. A Form 3115 (Change in Accounting Method) lets you take a catch-up deduction in a single current-year return. For investors who've accumulated $3M–$5M in properties over the past five years without studies, this look-back alone could generate $250,000–$500,000 in additional 2026 deductions.

The IRS processed over 14,000 cost segregation studies in 2024. That number is expected to roughly double in 2026 as awareness of the permanent bonus depreciation rule spreads. Cost seg firms are already reporting longer lead times heading into Q4. Investors who wait until October will face scheduling backlogs.

Common Mistakes Investors Make Here

• Skipping studies because the property "seems too small." Most CPAs informally set a $500K floor because the ROI is "borderline." But for investors in the 37% bracket with multiple properties, even a $300K property with a $1,200 condensed study can pencil out. Run the actual math before passing.

• Ignoring the passive loss trap. Bonus depreciation creates large paper losses. If your modified adjusted gross income (MAGI) exceeds $200,000, passive activity loss rules restrict your ability to use those losses against W-2 or other ordinary income — unless you qualify as a Real Estate Professional (750+ hours per year in real property trades, more than any other profession) or you own short-term rentals where you materially participate. Know your classification before you commission the study. Paper losses you can't use are not a tax strategy — they're deferred losses sitting on your return until you sell.

• Missing the short-term rental loophole. Short-term rentals with an average guest stay of 7 days or less are not classified as passive activities under the tax code. This means material-participant STR owners can offset ordinary income — including W-2 wages — with cost segregation losses, without needing REPS status. This is one of the most powerful (and underutilized) provisions in real estate tax planning.

• Not making a grouping election. If you own multiple rental properties, a grouping election on your tax return combines hours across properties for material participation purposes. This makes it significantly easier to hit REPS threshold or STR material participation standards without treating each property as a separate activity — a mistake that can make an otherwise eligible investor ineligible.

How to Use PropGPT for This

Prompt 1 — Quick cost seg ROI pre-flight:

"I'm buying a [residential/commercial] rental property for $[X] in [city, state]. The building was constructed in [year]. Estimate the likely cost segregation reclassification percentage I should expect, the year-one bonus depreciation deduction under the OBBBA, and my tax savings at a [X]% marginal rate. Show me a cost-benefit analysis vs. a study costing $2,000–$4,000."

This gives you a go/no-go decision before you've made a single phone call to a cost seg firm.

Prompt 2 — Passive loss eligibility audit:

"My MAGI is approximately $[X]. I own [N] rental properties and spend about [Y] hours per year on real estate activities. I'm not a full-time investor. Will bonus depreciation losses from a cost segregation study be usable against my ordinary income? Walk me through the passive activity loss rules and tell me what my options are — including REPS, the STR loophole, and grouping elections."

Prompt 3 — STR material participation analysis:

"I own a short-term rental in [city] with an average guest stay of [X] days. I self-manage and spent approximately [Y] hours on it last year. Can I use cost segregation losses from this property to offset my $[X] ordinary income without REPS status? Explain the STR material participation loophole and what contemporaneous documentation I need to support the deduction."

Prompt 4 — Look-back study opportunity:

"I purchased a [N]-unit apartment in [city] in [year] for $[X] and never did a cost segregation study. What missed depreciation could I recover with a look-back study in 2026? Explain how the Form 3115 catch-up deduction works and what it would look like on my 2026 tax return — without needing to amend prior-year returns."

Prompt 5 — Full portfolio cost seg analysis:

"I own [N] rental properties acquired between [year range] with a combined purchase price of $[X]. None have cost segregation studies. Estimate the total look-back depreciation opportunity across the portfolio, identify which properties to prioritize for 2026 studies based on property type and acquisition date, and flag any passive loss, REPS, or grouping election considerations I need to bring to my CPA."

The Bottom Line

The OBBBA handed real estate investors a permanent tax advantage that most W-2 earners will never have access to: the legal ability to zero out a six-figure income with paper losses from properties you already own — or are about to buy. 100% bonus depreciation is not going away. QBI is not going away. 1031 exchanges are untouched. The tax code is as favorable to real estate as it has been in decades.

But favorable tax law does nothing if you don't act on it. If you acquired property in 2025 or 2026 and haven't commissioned a cost segregation study, December 31, 2026 is your deadline — and cost seg firms book up in Q4. If you've been accumulating a portfolio for years without studies, a look-back analysis could mean six figures in legitimate retroactive deductions on your 2026 return without amending a single prior filing.

Use PropGPT to model the math first. Know your passive loss exposure, understand your REPS or STR situation, and walk into your CPA meeting already knowing what you're worth claiming. Then move.