179D Tax Deduction: Deadline, Amounts, and How to Claim

The 179D tax deduction is a federal write-off that lets commercial building owners immediately deduct the cost of energy-efficient improvements instead of depreciating them over decades. For the 2025 tax year, it runs from $0.58 to $5.81 per square foot, depending on how much energy the building saves and whether the project meets federal labor standards.¹ One date now overshadows every other decision around it: the One Big Beautiful Bill Act eliminated 179D for any property whose construction begins after June 30, 2026.²

The June 30, 2026 Deadline

Under Public Law 119-21, no 179D deduction is allowed for property whose construction begins after June 30, 2026.² The trigger is “begins construction,” not “placed in service.” A project that breaks ground or incurs at least five percent of total costs before July 1, 2026, should still qualify even if the building itself is completed months later. Plans still sitting on paper need to move.

Who Can Claim It

The primary claimants are commercial property owners that pay federal income tax: individuals, corporations, partnerships, and Real Estate Investment Trusts that own warehouses, offices, retail space, or large multi-family residential complexes (generally four or more stories). The owner claims the deduction in the year the energy-efficient property is placed in service, meaning installed and ready for use.³

Tax-exempt entities such as government agencies, tribal governments, and nonprofits owe no federal income tax and cannot use the deduction themselves. Instead, the law lets them allocate it to the project’s primary designer. Architects, engineers, and design-build contractors who produce the technical plans for a tax-exempt building can receive the benefit through a formal written allocation.⁴ The allocation is signed by an authorized representative of the owner and must include the name, address, and taxpayer identification number of both parties, the building’s square footage, and the placed-in-service date. For design firms working on schools, municipal buildings, and houses of worship, this is a real revenue stream.

What Qualifies as an Energy-Efficient Improvement

Improvements must cover at least one of three building systems: interior lighting, HVAC (including ventilation and hot water), or the envelope, meaning roof, walls, windows, and insulation. They also have to be part of a plan that reduces total annual energy and power costs by at least 25 percent compared to a reference building.⁴ Miss the 25 percent floor, even by a hair, and there is no deduction.

The reference building is a hypothetical version of your structure that meets the minimum requirements of ASHRAE Standard 90.1. For property placed in service before January 1, 2027, the applicable reference standard is ASHRAE 90.1-2007.³ That older baseline generally works in the taxpayer’s favor, since modern equipment clears it more easily.

One trap: the older partial deduction for standalone lighting (the “interim lighting rule”) does not exist for property placed in service after December 31, 2022.¹ A lighting-only upgrade no longer qualifies on its own. The whole-building 25 percent test applies regardless of which system you touch.

How Much the Deduction Is Worth

The amount scales with energy savings. At the statutory base, the deduction starts at $0.50 per square foot for a 25 percent reduction and rises by $0.02 for each additional percentage point, capping at $1.00 per square foot at 50 percent savings.⁴ Those base figures are indexed for inflation starting in 2023.

For 2025, the inflation-adjusted base range runs from $0.58 to $1.16 per square foot.¹ The IRS had not published 2026 inflation-adjusted figures at the time of writing.

The Bonus Tier

Projects that meet federal prevailing wage and apprenticeship rules qualify for a bonus roughly five times the base. The statute multiplies the figures: $2.50 per square foot at 25 percent savings, rising $0.10 per point, up to $5.00 at 50 percent savings.⁴ After inflation adjustments, the 2025 bonus range is $2.90 to $5.81 per square foot.¹

Put in real numbers: a 100,000-square-foot building achieving 50 percent savings with prevailing wage compliance could generate a deduction over $580,000 at 2025 rates. That is a reduction in taxable income, not a credit, so the actual tax savings depend on the owner’s marginal rate.

Prevailing Wage and Apprenticeship Rules

Qualifying for the bonus means meeting two labor standards during construction. All laborers and mechanics on the project must be paid at least the locally prevailing wage as determined by the Department of Labor under the Davis-Bacon Act.⁵ Rates vary by geography and trade classification, so pull the applicable wage determination before construction starts. Payroll records need to be meticulous, because the IRS requires a compliance statement attached to the tax return.⁶

For projects beginning construction after December 31, 2023, at least 15 percent of total labor hours must be worked by qualified apprentices from registered programs, and each contractor or subcontractor employing four or more workers on the project must employ at least one apprentice.⁷ The apprenticeship rules come from Section 45(b)(8), which 179D incorporates by cross-reference.

Get prevailing wage wrong and you can cure it: pay the affected worker the shortfall plus interest, plus a $5,000 per-worker penalty. If the IRS finds the failure was intentional, the penalty is three times the underpayment or $10,000 per worker, whichever is greater. These penalty rules come from Section 45(b)(7)(B).⁴ On a large project with dozens of tradespeople, sloppy payroll can produce six-figure penalties.

The Retrofit Pathway for Older Buildings

The Inflation Reduction Act created a separate route under Section 179D(f) for buildings originally placed in service at least five years before the retrofit plan is established. It measures actual reductions in energy use intensity (EUI) rather than modeled cost savings.⁴ For older buildings whose quirks make theoretical modeling unreliable, this is often the more accurate approach.

Using it requires a qualified retrofit plan, a written document prepared by a licensed architect or professional engineer that identifies the upgrades and certifies both the baseline and post-improvement EUI. The professional certifies the EUI within one year before the improvements are placed in service, then again more than one year after. The final certification must confirm the building’s EUI dropped to 75 percent or less of baseline, the same 25 percent minimum reduction.⁴ A building that already claimed 179D as new construction cannot later use the retrofit pathway for the same property.

Certification and Energy Modeling

No deduction is allowed without a formal certification from a qualified independent professional, a licensed engineer or architect not on your payroll. The professional inspects the completed building, verifies the systems were installed as designed, and certifies the energy reduction percentage.³

For the modeling pathway, the energy savings calculation must use software approved by the Department of Energy, which maintains an official list of qualified programs.⁸ Retrofit-pathway projects skip the modeling and rely on measured energy data.

The certification document should record the software version used, the building’s location, and the exact energy reduction achieved. Archive the technical specifications of the installed systems as well: R-values for insulation, efficiency ratings for HVAC, and lighting power densities. If the return is audited, that documentation is your defense. Professional fees for modeling and certification typically run $0.10 to $0.50 per square foot.

How to Claim It on Your Return

The deduction is reported on IRS Form 7205, Energy Efficient Commercial Buildings Deduction. Both owners and designers receiving an allocation file this form, which attaches to the annual income tax return. For a corporation, the deduction flows to Form 1120, line 25; for individuals and pass-throughs, it flows through to Form 1040.⁹

If you are claiming the bonus, attach a separate statement to the return establishing that you satisfied both the prevailing wage and apprenticeship requirements.⁶ You do not attach the energy certification or the designer allocation letter itself, but keep them for at least three years after filing.¹⁰ Given the size of most 179D claims, longer retention is prudent.

The Basis Reduction Trade-Off

Every dollar deducted under 179D reduces the tax basis of the improved property by the same amount.⁴ A $500,000 deduction today means $500,000 less basis at sale, which raises the taxable gain. The recaptured amount is treated as ordinary income rather than capital gains. For long-term holders, the time value of the upfront deduction generally beats the future recapture; for owners considering a near-term sale, run the math.

Recovering Missed Deductions From Prior Years

Owners who qualified in earlier years but never claimed 179D can usually recover the deduction by filing Form 3115, Application for Change in Accounting Method, treating the missed amount as a Section 481(a) adjustment. This picks up the full prior-year deduction on the current return without amending old ones.

Designers are treated differently. A 2025 Tax Court decision, Cannon Corp. v. Commissioner, held that designers cannot use Form 3115 because a designer’s allocation is not an acceleration of depreciation but a one-time deduction from a building the designer does not own. A designer who missed a prior year has to file an amended return for the year the property was placed in service, using Form 1040-X for individuals or the appropriate amended business return.

With the June 30, 2026 sunset in view, taxpayers with eligible projects already placed in service should review whether prior-year deductions are still on the table. The window to amend most returns is three years from the original filing date, so 2022 and 2023 projects may still be recoverable.

1
Department of Energy. 179D Energy Efficient Commercial Buildings Tax Deduction
2
Internal Revenue Service. FAQs for Modification of Sections 25C, 25D, 25E, 30C, 30D, 45L, 45W, and 179D Under Public Law 119-21
3
Internal Revenue Service. Energy Efficient Commercial Buildings Deduction
4
Office of the Law Revision Counsel. 26 USC 179D – Energy Efficient Commercial Buildings Deduction
5
U.S. Department of Labor. Davis-Bacon and Related Acts
6
Internal Revenue Service. Instructions for Form 7205 (Rev. December 2025)
7
Office of the Law Revision Counsel. 26 US Code 45 – Electricity Produced From Certain Renewable Resources
8
Department of Energy. Qualified Software for Calculating Commercial Building Tax Deductions
9
Internal Revenue Service. About Form 7205, Energy Efficient Commercial Buildings Deduction
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Internal Revenue Service. How Long Should I Keep Records