179D grandfather check - deduction dollars that survive the 2026 sunset
Does the project still clear the 2026-06-30 179D gate, and what is it worth on the 2026 rate table?
Gate result
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Days inside the 2026-06-30 gate
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days
2026 deduction rate
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per sq ft
179D deduction dollars still claimable
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dollars
45L credit on homes acquired in time
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dollars
Total still on the table
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dollars
Which return it goes on
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Checked this project? The full version writes a dated CSV of every project you check and sets alarms before each placed-in-service and amended-return window closes.
$60 once · one licence key per person or team seat · A third-party 179D engineering study with the site visit and energy model is commonly quoted at 5000 to 15000 dollars per building.
Begin construction gate Tests your construction start against the 2026-06-30 179D gate the One Big Beautiful Bill Act set. A start of 2026-05-15 lands 46 days inside the gate, so the project is grandfathered and the deduction dollars survive the 2026 sunset even when it is placed in service in 2027 or 2028.
2026 rate table Prices the deduction on the Rev. Proc. 2025-32 table for 2026: 0.59 to 1.19 per sq ft base, and 2.97 to 5.94 per sq ft where prevailing wage and apprenticeship are met or exempt. At 35 percent modeled savings the rate is 4.16 per sq ft, not the 2025 cap of 5.81.
Deduction dollars still claimable A 120000 sq ft grandfathered project at 4.16 per sq ft keeps 499200 deduction dollars that survive the 2026 sunset. The tool shows the figure next to the gate result so the number and the reason sit together.
45L homes on their own gate 45L runs on a separate test: homes acquired on or before 2026-06-30 still earn 2500 per ENERGY STAR home or 5000 per DOE Zero Energy Ready home. 12 Zero Energy Ready homes add 60000 on top of the 179D figure.
Portfolio export and window alarms The paid key writes a dated CSV row for every project you have checked and sets an alarm before each placed-in-service return and amended-return window closes.