Windows Depreciation Life: 27.5 vs. 39-Year Rules

Replacement windows on a rental or business property are treated as part of the building itself, so the windows depreciation life follows the building’s recovery period: 27.5 years for residential rental property and 39 years for nonresidential real property, both under the straight-line method. If you’re required to use the Alternative Depreciation System, those periods stretch to 30 and 40 years respectively.¹ The expected service life of the windows themselves doesn’t come into it.

When You Actually Have To Capitalize

Not every window expense gets spread over decades. The IRS tangible property regulations separate repairs, which you deduct in the year you pay for them, from capital improvements, which have to be depreciated. Window work falls on one side or the other under what’s called the Betterment, Adaptation, Restoration test.²

A window job is a betterment if it fixes a material defect or is a meaningful performance upgrade, such as swapping single-pane glass for double-pane energy-efficient units. It’s a restoration if you’re replacing a major structural component. Replacing all or most of the windows in a building almost always qualifies as a restoration, and either finding forces capitalization.³

The relevant “unit of property” for this test is the entire building structure, because windows are part of the structure and not a separate building system like plumbing or HVAC.¹ So you measure the work against the whole building, and even a partial replacement can trigger capitalization when the upgrade is substantial enough.

The Safe Harbors Rarely Rescue You

Two IRS safe harbors can sometimes let you expense what would otherwise be a capital cost, but neither is much help for windows. The de minimis safe harbor caps out at $2,500 per invoice, or $5,000 if you have audited financial statements. Any multi-window project blows past that. The routine maintenance safe harbor requires work you’d expect to perform more than once during the property’s class life, which for buildings means more than once every ten years.² Owners don’t replace windows on that cycle, so this one almost never fits.

How To Calculate the Annual Deduction

Real property, including capitalized window costs, uses straight-line depreciation. Divide the total capitalized cost by the number of years in the recovery period.¹ That works out to roughly 3.636% per year for 27.5-year residential rental property and about 2.564% per year for 39-year nonresidential property.

The mid-month convention adjusts the first and last year. The IRS treats the windows as placed in service at the midpoint of the month you actually put them into service, regardless of the exact date.¹ You get half a month in the first month, full months after that.

A quick example. You capitalize $100,000 in new windows on a commercial building and place them in service in December. A full-year deduction would be $2,564. Because you only had half a month of service in December, you’d deduct roughly $107 that first tax year ($2,564 × 0.5 ÷ 12).¹ IRS Publication 946 has percentage tables that handle the month-of-placement math for you.

Replaced windows start their own clock. They’re treated as a separate asset with their own placed-in-service date, but they stay in the same property class as the building.³ New windows on a duplex placed in service in 2026 get a fresh 27.5-year period from that month.

One boundary on the 27.5-year figure. If the building is mixed-use, at least 80% of gross rental income has to come from dwelling units for the whole building to qualify as residential rental property.⁴ Fall under 80% and the windows depreciate over 39 years instead.

Can You Write Windows Off Faster?

Most owners would rather not wait 27.5 or 39 years. The usual acceleration tools are Section 179, bonus depreciation, and Qualified Improvement Property treatment, and each of them runs into the same problem with windows.

Section 179 Expensing

Section 179 lets you deduct the full cost of qualifying property in the year of placement, up to an annual limit that’s inflation-adjusted. For 2026 the limit is approximately $2,560,000, with a phase-out starting when total qualifying property exceeds roughly $4,090,000. But Section 179 generally requires tangible personal property. Structural components of a building don’t qualify. The statute carves out a narrow category called “qualified real property,” covering QIP, roofing, HVAC, fire protection, and security systems.⁵ Windows are not on that list.

Bonus Depreciation

The One, Big, Beautiful Bill restored 100% bonus depreciation for qualified property acquired after January 19, 2025.⁶ Qualified property here means tangible property with a recovery period of 20 years or less, plus QIP. Real property depreciated over 27.5 or 39 years doesn’t clear the 20-year bar.

Why Windows Don’t Reach QIP

Qualified Improvement Property has a 15-year recovery period and is the escape hatch that lets certain improvements pick up both Section 179 and bonus depreciation. QIP means any improvement to the interior of a nonresidential building made after the building was first placed in service, and it specifically excludes building enlargements, elevators, escalators, and changes to internal structural framework.¹ Windows are exterior envelope, not interior. That knocks them out of QIP in nearly every scenario, even when the windows go in as part of a broader interior remodel. Absent a QIP-qualifying angle, the standard 27.5-year or 39-year straight-line schedule is what you have.

Claim the Loss on the Old Windows

This is where a lot of owners leave money behind. When you pull out the old windows, they still have undepreciated basis sitting on your books. A partial disposition election lets you deduct that remaining basis as a loss.⁷

The election treats the removal as a disposition event. Depreciation on the old windows stops and you recognize a loss equal to their adjusted basis. You make the election by reporting the loss on your return for the year the old windows come out, and the deadline is the due date of that return including extensions.⁷

The hard part is figuring out what the old windows originally cost, especially if the building was bought years ago and the windows were never priced out separately. The IRS accepts several reasonable reconstruction methods, including a Producer Price Index discount from the current replacement cost (available only when the work is a restoration), a pro rata allocation from the building’s original cost, or a full component study. Once you have that original cost, subtract the depreciation that was allowed or allowable, and what remains is your deductible loss.⁸ On a building held only a portion of its recovery period, that number can absorb a real slice of the new window cost.

Blinds and Shades Are a Separate Asset

Window treatments aren’t windows. Blinds, shades, and decorative shutters that aren’t permanently attached to the building structure are generally tangible personal property, not structural components. Furnishings used in residential rental activity fall into the 5-year MACRS class; office furniture and fixtures land in the 7-year class.¹

The difference is significant. Custom blinds worth $8,000 in a rental recover over five years instead of 27.5, and personal property classification also opens the door to Section 179 and bonus depreciation. Ask your installer to itemize the invoice so window costs and treatment costs stay separated, and each piece can be depreciated on its own schedule.

Energy-Efficient Windows on Commercial Buildings

Commercial owners and large multifamily owners have one more tool. The Section 179D deduction allows a per-square-foot deduction for energy-efficient improvements to the building envelope, which includes windows. For 2025, it ranges from $0.58 to $5.81 per square foot depending on the energy savings achieved and whether prevailing wage and apprenticeship rules are met. The project has to hit at least 25% energy savings against a reference standard to qualify at all.⁹

There’s a deadline. The current version of Section 179D doesn’t apply to property whose construction begins after June 30, 2026.⁹ A commercial window upgrade that could clear the 25% threshold needs to get moving before that date.

What Goes Into the Capitalized Cost

What you depreciate isn’t just the invoice for the glass. Capitalized cost includes everything needed to put the windows into service: the windows themselves, sales tax on materials, delivery charges, and the full cost of professional installation labor. Installation labor alone commonly runs $140 to $400 per window depending on type and complexity. Keep detailed invoices, and keep window costs separated from any unrelated work done at the same time, so the amount you capitalize is right and no deductible repair gets buried inside a 27.5-year schedule.

1
Internal Revenue Service. Publication 946 (2025), How To Depreciate Property
2
Internal Revenue Service. Tangible Property Final Regulations
3
Internal Revenue Service. Depreciation and Recapture 4
4
Internal Revenue Service. Publication 527 (2025), Residential Rental Property
5
Office of the Law Revision Counsel. 26 USC 179 – Election To Expense Certain Depreciable Business Assets
6
Internal Revenue Service. Treasury, IRS Issue Guidance on the Additional First Year Depreciation Deduction Amended as Part of the One, Big, Beautiful Bill
7
eCFR. 26 CFR 1.168(i)-8 – Dispositions of MACRS Property
8
Internal Revenue Service. Examining a Taxpayer Electing a Partial Disposition of a Building
9
Department of Energy. 179D Energy Efficient Commercial Buildings Tax Deduction