179D and 45L Changed: Check the Right Date Before You Rely on an Old Article.
Quick answer: The June 30, 2026 date applies differently to these two provisions. Read the trigger, not just the headline.
An older guide can describe a valuable incentive and still mislead you about a new project. As of this article’s October 8, 2026 source check, the IRS describes accelerated termination rules for both 179D and 45L. Start by identifying which provision you are discussing and which event controls its cutoff.
Two provisions, two different triggers
The IRS states that 45L is not allowed for qualified new energy-efficient homes acquired after June 30, 2026. For 179D, the deduction is not allowed for property whose construction begins after June 30, 2026. These are different tests. A single calendar date does not make the acquisition event and construction-start event interchangeable.
Build a date file before a benefit estimate
For a professional conversation, prepare a timeline supported by the relevant agreements and project records. Identify which facts are certain and which need interpretation. Ask the reviewer to apply the legal meaning of the controlling event to your circumstances. Do not assume that reserving a project, purchasing land or arranging finance answers a different date question.
Use examples as questions, not rulings
Imagine one developer with an older project and another beginning a new project after the cutoff. Their conversations may be different even if the buildings have similar energy features. These hypothetical examples are not conclusions about eligibility. Ask the reviewer which facts and certifications are still required and whether the relevant cutoff has been satisfied.
An earlier date does not settle every requirement
Meeting a timing condition is only one part of the discussion. Ask who can assess the remaining technical and tax requirements and what documentation is needed. A dated project file makes that review more efficient, but it should not be treated as automatic approval. Request an explanation that your return preparer can use.
Check the age of the information you share
Before sending a guide to your team, look for its source date and current IRS reference. If an article still assumes a much later expiration date without addressing the change, pause before using it to make a decision. Keep a note of the source you relied on and ask your adviser to verify later developments.
Your next step
Read the IRS termination FAQ linked below, then take your date file to a qualified professional. Do not use this site’s R&D referral form for an energy-incentive project.
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Sources and editorial notes
IRS primary-source reference. Sources checked October 8, 2026. Examples are hypothetical; people shown are AI-generated illustrations, not clients or endorsers. This article provides general education and has not been represented as reviewed by a tax professional. Eligibility and outcomes depend on your facts and current rules.