1. What a cost segregation study does
A building normally depreciates over 27.5 years (residential) or 39 years (commercial). A cost segregation study breaks the purchase price apart and reclassifies components like flooring, cabinetry, dedicated electrical, and land improvements into 5, 7, and 15-year property, so a large slice of the basis depreciates on much shorter schedules.
On the federal return, that reclassified property also qualifies for bonus depreciation, which restores a 100% first-year write-off for qualifying property acquired and placed in service after January 19, 2025. States set their own rules, which is where Oklahoma comes in.
2. Oklahoma and federal bonus depreciation
Oklahoma starts from federal adjusted gross income with rolling IRC conformity and requires no addback of current-law IRC 168(k) bonus depreciation for individuals or corporations, so the OBBBA's permanent 100% bonus for property acquired after January 19, 2025 flows straight through to the Oklahoma return. Oklahoma went further than conformity: HB 3418 (signed May 26, 2022) enacted 68 O.S. 2358.6A, making Oklahoma the first state with its own PERMANENT 100% full-expensing election for IRC 168(k)-defined qualified property and qualified improvement property placed in service in tax years beginning after December 31, 2021, regardless of what federal law allows. During the federal phase-down (60% in 2024, 40% for property placed in service January 1-19, 2025), Oklahoma taxpayers could still elect 100% expensing on the state return, deducting the full cost in the placed-in-service year and adding back the federal depreciation claimed on that property in later years (OAC 710:50-21-5; the election is irrevocable). Post-OBBBA the federal and Oklahoma deductions are identical for most new acquisitions, so no adjustment is needed; the state election remains as a backstop if federal percentages ever drop again.
Worked example
A $1,000,000 building, with and without a study
Illustrative only. A residential rental purchased for $1,000,000 of building basis (land excluded), acquired and placed in service after January 19, 2025.
Building basis
$1,000,000
Reclassified to 5, 7, and 15-year property (25%)
$250,000
Federal first-year deduction at 100% bonus
$250,000
Year 1 on that $250,000 without a study (27.5-year straight line)
about $9,100
Oklahoma conforms to federal bonus depreciation, so the state return mirrors the $250,000 first-year deduction.
Model your own numbers with the tax strategy projector.
3. Section 179 in Oklahoma
Full conformity via rolling IRC adoption; no Oklahoma-specific cap or adjustment. Oklahoma automatically picks up the OBBBA increase to a $2.5 million deduction limit with a $4 million phase-out threshold (indexed) for property placed in service in tax years beginning after December 31, 2024. Tax Foundation estimated the automatic 179 expansion costs Oklahoma only $4-6 million per year, and the legislature made no move to decouple in the 2025 session.
4. Does it still help in Oklahoma?
Yes, and in Oklahoma it works at full strength: reclassified 5-, 7-, and 15-year MACRS property gets both federal AND Oklahoma 100% first-year expensing, since the state follows federal MACRS recovery periods and classifications (5/7/15/27.5/39-year) with no depreciation modification on current-law property.
- •Oklahoma was the FIRST state to enact permanent 100% full expensing (HB 3418, signed May 26, 2022; 68 O.S. 2358.6A), effective for tax years beginning after Dec 31, 2021, independent of federal phase-downs; 'qualified property' uses the IRC 168(k) definition, so cost-seg 5/7/15-year assets and QIP qualify
- •If the state full-expensing election is used when federal bonus is below 100% (e.g. 2024's 60% or Jan 1-19, 2025's 40%), the taxpayer deducts 100% on the Oklahoma return, then adds back the federal depreciation claimed on that property in later years; the election is irrevocable per OAC 710:50-21-5
- •The legacy 80% bonus addback in 68 O.S. 2358.6 (recovered 25%/yr over the following 4 years) applied only to corporations and only to bonus under the 2002 JCWAA, 2008 Economic Stimulus Act, and 2009 ARRA, so it does not touch TCJA/OBBBA-era property, but it still generates confusion and occasional erroneous OTC notices
- •HB 2764 (signed May 28, 2025) cuts the top individual rate from 4.75% to 4.5% for tax year 2026, collapses the brackets, and sets revenue triggers for 0.25-point reductions toward eventual phase-out, so state-side depreciation deductions are worth slightly less each triggered step
- •Oklahoma made no move to decouple from any OBBBA expensing provision in the 2025 legislative session; Tax Foundation scored 168(k) conformity at $0 cost to the state precisely because Oklahoma already had permanent full expensing
5. The exit: recapture and timing
The accelerated deductions come back into view when you sell. Gain attributable to the 5, 7, and 15-year property is Section 1245 recapture, taxed at ordinary rates, and the straight-line depreciation on the building itself is unrecaptured Section 1250 gain, taxed at up to 25%. A study does not create that bill, it moves deductions forward, but the timing of the sale decides how much of the benefit you keep.
Two levers manage the exit. A 1031 exchange defers both flavors of recapture along with the rest of the gain, and simply holding the property lets the time value of the early deductions do its work; most owners want a 3 to 5 year horizon before a taxable sale for the math to stay comfortably positive. Model the exit before you commission the study, not after.