The depreciation life of a commercial building is 39 years under the IRS General Depreciation System, which is what most owners use.1Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System You divide the building’s depreciable basis by 39 and deduct roughly that amount each year, straight-line, for nearly four decades. The structure itself is locked into that timeline. But interior improvements, several building systems, and many individual components can be written off far faster, and 2025 legislation made those accelerated paths considerably more generous.
What the 39-Year Rule Covers
Internal Revenue Code Section 168 puts nonresidential real property into a 39-year class covering any building used for business that isn’t residential rental property.1Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System Office buildings, warehouses, retail stores, medical facilities, restaurants, and self-storage buildings all land here.
The residential boundary matters. If dwelling units generate 80% or more of a building’s rental income, it’s residential rental property and follows a 27.5-year schedule instead. Mixed-use buildings can tip from one category to the other based on the income split, so the classification isn’t purely architectural.
Recovery uses the straight-line method: same deduction each full year, no front-loading and no declining balance.2Internal Revenue Service. 2025 Instructions for Form 4562 – Depreciation and Amortization A building with an $800,000 depreciable basis produces about $20,512 in annual depreciation. Predictable, but modest against the purchase price. The rest of this article covers the legal ways to speed things up.
When the 39-Year Clock Starts
Depreciation doesn’t begin at closing. It begins when the building is “placed in service,” meaning ready and available for its intended income-producing use. Buy in October, finish renovations in March, and depreciation starts in March. The trigger is functional readiness, not ownership.
For most purchases of already-operating buildings, closing and placed-in-service line up. Gut renovations, use conversions, and new construction push the date later. A certificate of occupancy, the first signed lease, or listings marketing the space as available all support the start date if the IRS questions it.
The Mid-Month Convention
Commercial buildings use the mid-month convention. The IRS treats the property as placed in service at the midpoint of the month it actually becomes available, so you claim a half-month of depreciation for that month plus full months for the rest of the year. Placed in service in August? That’s 4.5 months of first-year depreciation.3Internal Revenue Service. Publication 946 – How To Depreciate Property The same rule applies in reverse when you sell: depreciation runs through the midpoint of the disposal month, then stops. First and last years always produce smaller deductions than the years between.
Land Isn’t Depreciable
Only the structure qualifies for cost recovery. Land is never depreciable.4Internal Revenue Service. Topic No 704 – Depreciation When you buy commercial property, you have to split the purchase price between the two, and that allocation drives every deduction for the next 39 years.
Most owners use either a professional appraisal or the ratio in the local property tax assessor’s records. Buy for $1,000,000 with the assessor putting land at 20%, and your depreciable basis is $800,000. The IRS doesn’t mandate a specific method, but the split has to be reasonable and defensible. Understating land to inflate depreciation is a fast way to attract audit attention.
Qualified Improvement Property: 15 Years
Not every dollar spent on a commercial building sits in the 39-year bucket. Qualified Improvement Property (QIP) covers interior improvements made after the building was originally placed in service, and QIP has a 15-year recovery period.5Internal Revenue Service. Rev Proc 2020-25 New interior walls, updated lighting, flooring, ceiling systems, and tenant build-outs typically qualify. The CARES Act fixed a drafting error in the Tax Cuts and Jobs Act and made the 15-year period retroactive to property placed in service after 2017.
Several categories of work are excluded from QIP treatment:
- Enlargements that add square footage to the building.
- Elevators and escalators, which stay on the 39-year schedule.
- Internal structural framework such as load-bearing walls and columns.
The distinction matters most on large renovations mixing structural work with cosmetic upgrades. Careful line-item categorization on the contractor’s invoices can move dollars from a 39-year write-off to a 15-year one.
100% Bonus Depreciation After the OBBBA
The One Big Beautiful Bill Act permanently restored 100% bonus depreciation for qualifying property acquired and placed in service after January 19, 2025.6Internal Revenue Service. One Big Beautiful Bill Provisions Before the Act, bonus depreciation had been dropping 20 percentage points per year from its 100% level and was headed for zero by 2027. It’s now back to 100% with no scheduled sunset.
The 39-year building shell is not eligible for bonus depreciation. But QIP placed in service after January 19, 2025, is, meaning you can potentially deduct the full cost of an interior renovation in the year it’s completed rather than spread it over 15 years. Personal-property components identified by a cost segregation study also qualify.
Section 179 for Building Systems
Section 179 lets you deduct the full cost of qualifying assets in the year they’re placed in service. The 2026 deduction limit is $2,560,000, with a phase-out beginning when total qualifying purchases exceed $4,090,000. The building shell doesn’t qualify, but several systems do when they improve nonresidential real property already in service:3Internal Revenue Service. Publication 946 – How To Depreciate Property
- Roofs.
- HVAC systems.
- Fire protection and alarm systems.
- Security systems.
Qualified Improvement Property also qualifies for Section 179. The practical differences from bonus depreciation: Section 179 is capped annually and can’t create a net loss, while bonus depreciation has no dollar cap and can generate a loss. Most tax advisors run both approaches to see which produces a better result for the year.
Cost Segregation
A cost segregation study is the single most effective tool for accelerating commercial building depreciation. An engineering-based analysis breaks the property into its component parts and reclassifies items that don’t need to sit on the 39-year schedule. Electrical outlets, carpeting, decorative finishes, certain plumbing fixtures, and non-structural elements can shift into 5-year or 7-year personal property. Parking lots, sidewalks, fences, and landscaping typically become 15-year land improvements.3Internal Revenue Service. Publication 946 – How To Depreciate Property
With 100% bonus depreciation permanently back, everything reclassified into a 5-, 7-, or 15-year class can be fully deducted in year one. On a $3 million building, a typical study might reclassify 20% to 40% of the price into shorter-lived categories, producing $400,000 or more in first-year deductions against roughly $77,000 under straight 39-year depreciation. The study itself usually costs a few thousand dollars, which makes the math work for most buildings above roughly $1 million.
If you’ve owned a building for years and never had a study done, you can still benefit. Filing Form 3115 lets you change your depreciation method and catch up on missed deductions in a single tax year rather than amending prior returns.7Internal Revenue Service. About Form 3115 – Application for Change in Accounting Method
When You’re Stuck With 40 Years: ADS
Some owners have to use the Alternative Depreciation System instead of GDS. Under ADS, nonresidential real property stretches to 40 years rather than 39.3Internal Revenue Service. Publication 946 – How To Depreciate Property ADS still uses straight-line, so the practical differences are the extra year and the loss of bonus depreciation eligibility on certain property.
The most common trigger is the Section 163(j) election. Real property businesses that elect out of the business interest expense limitation get to deduct more interest, but they must use ADS for their real property in exchange.8eCFR. 26 CFR 1.163(j)-9 – Elections for Excepted Trades or Businesses That election is irrevocable, so model it carefully before committing. Tax-exempt use property and property used predominantly outside the United States are on ADS regardless of any election.
Depreciation Recapture at Sale
Every depreciation dollar claimed reduces your tax basis, and when you sell, the IRS wants some of that benefit back. For commercial real property, recaptured depreciation is taxed as unrecaptured Section 1250 gain at a maximum federal rate of 25%, higher than the long-term capital gains rate that applies to the remaining profit.9Internal Revenue Service. Topic No 409 – Capital Gains and Losses The sale and recapture get reported on Form 4797.10Internal Revenue Service. 2025 Instructions for Form 4797 – Sales of Business Property
Recapture applies to all depreciation claimed, including bonus depreciation and Section 179 amounts. Owners who accelerate hard through cost segregation get big upfront deductions and a correspondingly bigger recapture bill later. A 1031 like-kind exchange can defer both capital gains and recapture by rolling proceeds into a replacement property, though the existing depreciation schedules carry over rather than resetting.
Fixing Wrong or Missed Depreciation
If you’ve used the wrong recovery period, the wrong method, or haven’t claimed depreciation at all, the fix is Form 3115, Application for Change in Accounting Method.7Internal Revenue Service. About Form 3115 – Application for Change in Accounting Method This isn’t an amended return. It recalculates what depreciation should have been from the beginning and applies a cumulative Section 481(a) adjustment to the current year.
One trap worth flagging: the IRS treats depreciation as claimed whether you actually took it or not. Skip depreciation for years, then sell, and your basis is still reduced by what you were entitled to claim. You pay recapture on deductions you never benefited from. Filing Form 3115 before a sale corrects this by making sure you actually receive the deduction before the recapture comes due.