Section 179D Energy Deduction Calculator 2026
Estimate your Section 179D deduction for energy-efficient commercial buildings by entering square footage, deduction tier, and tax bracket. Cites IRS IRC §179D.
What Is the Section 179D Deduction?
Section 179D of the Internal Revenue Code allows owners and designers of energy-efficient commercial buildings to deduct the cost of qualifying energy improvements in the year they are placed in service, rather than depreciating them over 39 years. The deduction is calculated on a per-square-foot basis and ranges from $1.00 to $5.00 per square foot depending on the energy efficiency level achieved, as updated by the Inflation Reduction Act of 2022 (IRA).
Qualifying systems include HVAC, hot water, interior lighting, and the building envelope. The energy savings must be certified by a licensed engineer using an IRS-approved energy simulation software (such as eQUEST or EnergyPlus). The certification must compare the building to a baseline defined by ASHRAE Standard 90.1. Source: IRC §179D and IRS Notice 2023-29. Last updated: May 2026.
Section 179D Deduction Tiers (2026)
| Tier | Energy Reduction vs ASHRAE | Rate / Sq Ft | Prevailing Wage Required |
|---|---|---|---|
| Base (Partial) | 25-39% | $1.00 | No |
| Interim | 40-49% | $2.50 | Recommended |
| Full Bonus | 50%+ | $5.00 | Yes — prevailing wage + apprenticeship |
For a 100,000 sq ft warehouse at the $5.00 rate, the deduction is $500,000. At a 35% tax rate, this saves $175,000 in federal taxes in a single year. Without §179D, the same improvements would be depreciated over 39 years — yielding a much smaller annual deduction.
Who Claims the 179D Deduction?
Private commercial building owners claim the deduction directly. For government-owned buildings (federal, state, local), the owner cannot claim a tax deduction — instead, the deduction is "allocated" to the designer (architect, engineer, or contractor) who created the energy-efficient design. This designer allocation provision was expanded by the IRA to include non-profit organizations, tribal governments, and tax-exempt entities as building owners. Always retain a copy of the §179D certification signed by a qualified engineer for at least 7 years in case of IRS audit.
Section 179D vs Section 45L vs ITC
Section 45L applies to energy-efficient residential dwellings (up to $5,000 per unit for new construction). The Investment Tax Credit (ITC) under §48 applies to solar and specific energy systems — it is a credit, not a deduction. Section 179D is exclusively for commercial buildings. These can sometimes be stacked, but coordination rules reduce the 179D deduction by the ITC amount allocated to the same system. Model all three with your CPA to identify the optimal combination.
Frequently Asked Questions
Who qualifies for the Section 179D deduction?
Building owners of qualifying commercial buildings placed in service, and designers (architects, engineers) of energy-efficient systems in government buildings. The Inflation Reduction Act of 2022 expanded eligibility to non-profit organizations and tribal governments. Source: IRS Notice 2023-29 and IRC §179D.
What is the maximum Section 179D deduction per square foot in 2026?
For 2026, the maximum deduction is $5.00 per square foot for buildings meeting the highest energy efficiency standard (50%+ energy reduction versus ASHRAE 90.1 baseline), using prevailing wage and apprenticeship requirements. The base rate is $1.00/sq ft. Source: IRC §179D as amended by the Inflation Reduction Act.
What building systems qualify for Section 179D?
HVAC systems, hot water systems, interior lighting systems, and the building envelope (insulation, windows, doors, roofing) are all qualifying systems. The energy model must certify a 25-50% energy cost reduction versus ASHRAE 90.1 baseline to qualify at the $1.00-$5.00 range.
Is Section 179D a credit or a deduction?
Section 179D is a tax deduction, not a credit. It reduces taxable income. At a 21% corporate rate, a $500,000 deduction saves $105,000 in taxes. At a 37% individual rate, the same deduction saves $185,000. A credit is worth more dollar-for-dollar; a deduction's value depends on your marginal rate.
Does Section 179D apply to residential rental property?
No. Section 179D applies only to commercial buildings. Residential rental property of 4 or more units may qualify if it is 4 stories or more above grade. Mixed-use buildings may qualify for the commercial portion.
Can Section 179D be combined with other energy credits?
Yes, with coordination rules. Section 179D can be used alongside the Investment Tax Credit (ITC) for solar, but the 179D deduction amount must be reduced by the ITC amount allocated to the same system. Consult a tax professional to model the combined benefit.