Real Estate Tax Calc
How they interact
A cost segregation study identifies components of a building that qualify as 5-, 7-, or 15-year MACRS property. Bonus depreciation is then applied to those components in year one, allowing you to deduct a large percentage immediately rather than spreading the cost over years. The building's 27.5- or 39-year structural portion is ineligible for bonus — only the shorter-life components a cost seg study unlocks qualify.
A worked example
Suppose a $900,000 commercial building with a cost seg study identifies 25% as shorter-life property ($225,000). With a 40% bonus depreciation rate, you could deduct $90,000 in bonus depreciation in year one on those components, plus accelerated MACRS on the remainder. Without cost seg, the entire $900,000 would spread over 39 years with no bonus available — about $23,077/year.
Declining bonus rates change the math
Bonus depreciation phases down annually. At 100%, cost seg could create a near-complete immediate write-off of qualifying components; at lower rates, the first-year benefit shrinks. Acting earlier in the phase-down schedule captures more of the benefit. Confirm the current-year rate before structuring a purchase.
What bonus depreciation actually is
Bonus depreciation (Section 168(k)) is a first-year deduction that lets you expense a set percentage of the cost of qualifying property in the year you place it in service, instead of recovering it gradually. It applies to property with a MACRS recovery period of 20 years or less — which is exactly the 5-, 7-, and 15-year classes a cost segregation study carves out of a building. The 27.5-year (residential) or 39-year (nonresidential) structural shell has a recovery period over 20 years, so it never qualifies for bonus. That single fact is why the two strategies are joined at the hip: cost segregation manufactures the short-life property, and bonus depreciation supercharges it.
The phase-down schedule and the 2025 reset
Under the 2017 Tax Cuts and Jobs Act, bonus was 100% for property placed in service from late September 2017 through 2022, then scheduled to step down: 80% in 2023, 60% in 2024, 40% in 2025, 20% in 2026, and 0% after 2026. In 2025, federal legislation revisited that schedule and restored 100% bonus depreciation for qualifying property placed in service after a specified 2025 date. Because the applicable percentage turns entirely on your placed-in-service year — and the law here has changed more than once — never assume a headline rate. Confirm the exact percentage for your year with your CPA before you model a purchase or sign a study engagement.
Which components qualify — and QIP
A study typically reclassifies 5-year property (carpeting, appliances, decorative fixtures, cabinetry, certain electrical and plumbing tied to specific equipment), 7-year property (certain furniture and equipment), and 15-year land improvements (paving, sidewalks, fencing, landscaping, site utilities). A separate category, Qualified Improvement Property (QIP) — interior, non-structural improvements to nonresidential buildings made after they were first placed in service — was assigned a 15-year life by the CARES Act correction, making it bonus-eligible as well. All of these fall under the 20-year threshold, so each dollar reclassified into them is a dollar that can be bonus-expensed.
Section 179 vs. bonus depreciation
Section 179 expensing and bonus depreciation both accelerate deductions, but they differ in important ways. Section 179 has an annual dollar cap and a phase-out once total qualifying purchases exceed a threshold, and — critically — it cannot create or increase a loss (it is limited to business taxable income). Bonus depreciation has no dollar cap and can create a loss, which is exactly what real estate investors want when the goal is to offset other income. Section 179 also historically did not apply to residential rental property held for the production of income in the same way. For most cost-seg-driven rental strategies, bonus depreciation is the workhorse and Section 179 is a supplement, if used at all.
Worked example: 100% vs. 40% bonus
Return to the $900,000 building with $225,000 reclassified into short-life property. At 100% bonus, you deduct the full $225,000 in year one (plus first-year MACRS on the structural shell). In a 32% bracket, that is roughly $72,000 of first-year federal tax deferred from the components alone. At 40% bonus, only $90,000 of the $225,000 is bonus-expensed; the remaining $135,000 recovers over its 5-/7-/15-year MACRS schedule. The first-year component deduction drops to about $90,000 plus a partial-year MACRS slice on the balance — perhaps $110,000–$120,000 total instead of $225,000. Same study, same building, same reclassification — the placed-in-service year alone roughly halves the first-year benefit.
State conformity can mute the federal win
Many states decouple from Section 168(k). They require you to add the federal bonus amount back to state income and depreciate those components on a slower state schedule, creating a permanent federal/state basis difference you must track for the life of the asset. States such as California do not allow bonus depreciation at all for corporate/personal income tax purposes. If a large share of your total tax burden is at the state level, the federal headline number overstates your real, all-in benefit. Always model federal and state separately before deciding a study is worth it.
The catch: 1245 recapture at sale
Bonus depreciation and cost segregation front-load deductions, but they do not make the tax disappear — they defer it. The reclassified 5-, 7-, and 15-year components are Section 1245 property, and the depreciation taken on them is recaptured as ordinary income at sale, with no 25% cap. If you accelerate $225,000 of deductions and later sell without a 1031 exchange or a step-up at death, much of that acceleration returns as ordinary-rate recapture. The strategy shines when you hold long term, exit via a 1031 exchange, or hold until death (when heirs receive a stepped-up basis that erases the built-in recapture). It works against you on a quick flip in a high bracket.
You still need to be able to use the loss
The single biggest mistake investors make is assuming a giant first-year deduction automatically lowers their tax. It only does if the loss is not trapped by the passive activity rules. Rental losses are passive by default and offset only passive income — unless you qualify as a real estate professional and materially participate, or run a short-term rental (average stay of seven days or less) in which you materially participate. High earners are also phased out of the $25,000 active-participation allowance above $150,000 of modified AGI. Pair a bonus-charged cost seg study with a passive investor who cannot use the loss, and the deduction simply suspends and carries forward — you get the timing benefit only when you sell or generate passive income. Confirm you can use the loss before you pay for the study.
Placed-in-service timing controls the deduction year
Bonus depreciation is claimed in the year the property is placed in service — ready and available for its intended use — not necessarily the year you bought it or the year the study is finished. Close on a building in December but fail to make it available for rent until January, and the entire first-year write-off shifts to the following tax year (and possibly a different bonus percentage). For new construction or a substantial renovation, the placed-in-service date is when the certificate of occupancy is issued or the space is genuinely ready. Because the applicable bonus rate can differ year to year, this timing can swing the deduction by tens of thousands of dollars.
Lookback studies via Form 3115
You do not have to perform a cost segregation study in the year of purchase. A lookback study on a property you have owned for years reclassifies components as if the correct classification had been used from the original placed-in-service date. The cumulative under-claimed depreciation — including bonus that would have applied — is recovered in the current year as a Section 481(a) adjustment on Form 3115 (Application for Change in Accounting Method), with no need to amend prior returns. Note that bonus depreciation on the catch-up is generally driven by the bonus rate that applied in the original placed-in-service year, so a property placed in service during a 100% bonus window can produce a large catch-up deduction today.
A quick decision checklist
Before pairing a study with bonus depreciation, run these questions: What bonus percentage applies in my placed-in-service year under current law? How much of the basis is realistically reclassifiable into 20-year-or-less property? Can I actually use the resulting loss this year (REPS, STR, or passive income), or will it suspend? Does my state conform to bonus, or will I carry a basis difference? How long will I hold, and will I 1031 or step up at death to defer the 1245 recapture? When the answers line up — high usable bracket, high building-to-land ratio, meaningful bonus rate, long hold or deferred exit — the combination is one of the most powerful tools in real estate tax. When they don't, the study fee may outrun the benefit.
Frequently asked questions
Does the entire building qualify for bonus depreciation?
No — only the shorter-life components a cost seg study identifies. The building's 27.5- or 39-year structure must use straight-line MACRS with no bonus.
How does a declining bonus rate affect cost seg value?
A lower bonus rate reduces the first-year deduction but doesn't eliminate the value of a faster MACRS schedule on the reclassified components.
What property qualifies for bonus depreciation?
Property with a MACRS recovery period of 20 years or less — the 5-, 7-, and 15-year classes and Qualified Improvement Property. The 27.5-/39-year building shell does not qualify.
Is bonus depreciation better than Section 179 for rentals?
Usually, yes. Bonus has no dollar cap and can create a loss to offset other income, while Section 179 is capped and limited to business taxable income (it cannot create a loss).
Do I have to pay the bonus depreciation back when I sell?
Effectively, yes, unless you defer it. Depreciation on 1245 components is recaptured as ordinary income at sale — but a 1031 exchange or a step-up in basis at death can defer or eliminate that recapture.
Can I still benefit if my state doesn't conform to bonus?
Yes, at the federal level. But decoupled states make you add the bonus back and depreciate slower, so your combined federal-plus-state benefit is smaller than the federal number alone suggests.
Sources
Educational information and estimates only. Not tax advice. Tax rules change and vary by situation; consult a qualified tax professional before acting.