Two years of tax content has described the One Big Beautiful Bill Act with a coin-flip of dates: “the Senate passage date,” “the July 4 signing date,” “January 2025.” Only one of those is the date the statute actually uses, and it’s the one that decides whether your biggest deduction is 100% of your reclassified basis or roughly a fifth of it.

What §70301 did, precisely

Reading the statute (P.L. 119-21, §70301): it sets the §168(k) applicable percentage to 100% permanently by striking the phase-down paragraphs that would have walked 100 → 80 → 60 → 40 → 20 → 0. The 100% rate applies to qualified property acquired after and placed in service after January 19, 2025 — a date written into the statute itself. (For the record: the Senate voted on July 1, 2025; the January 19 date has nothing to do with that vote. Any article calling January 19 “the Senate passage date” copied a transcript, not a statute.)

For real estate investors the practical machinery is:

  • Purchase deals: the binding-contract date controls acquisition — the point your purchase contract became enforceable (deposit, contingencies waived, or as Notice 2026-11’s framework applies the §1.168(k)-2 rules). Not closing day. Not the funding date.
  • Owner builds / self-constructed: construction-start timing controls instead of any contract — different test, same January 19 line.
  • Placed in service must also be after January 19, 2025. A December 2024 closing under a November contract doesn’t get 100% bonus just because it closed later.

The fallback for pre-cutoff contracts

Property acquired under a binding contract on or before January 19, 2025 keeps the old TCJA phase-down by placed-in-service year: 40% for 2025 (60% for certain property with long production periods), a further-reduced figure for 2026, and 0 thereafter — Notice 2026-11 explicitly governs the 2025 in-service case. Fiscal-year filers get a transition election (new §168(k)(10)) to apply 40% (or 60%) for the first tax year ending after January 19, 2025. These elections are real money; your CPA should make them with full asset data in hand — another reason the study should be done before the return is filed, not retroactively in panic.

The stack nobody else spells out: bonus + cost seg + 163(j)

Bonus depreciation multiplies what a cost segregation study is worth, because the study decides how much of your purchase price is qualified property that rides the 100% lane. A 30% reclassification on a $2M acquisition is roughly $600K of year-one write-off on a post-cutoff deal — before the shell’s regular MACRS.

And OBBBA quietly removed the penalty that used to make big-depreciation years expensive: the §163(j) business-interest limitation is back to an EBIT basis — depreciation no longer reduces your interest-deduction capacity, permanently, for tax years beginning after 2024. The IRS updated its FAQs on December 23, 2025. Translation for leveraged investors: a heavy cost-seg year no longer “costs” you leverage capacity. That is a big deal for portfolio borrowers, and most explainers still haven’t mentioned it.

Two live 2026 items to know

  1. Notice 2026-11 is the interim rule examiners are applying right now for OBBBA bonus questions — expect proposed regs to follow; until then, document your binding-contract dates like an auditor will ask (they will).
  2. New §168(n) lets owners of nonresidential buildings used integrally in qualified production activities elect a 100% first-year deduction on the qualifying portion (construction begins 2025–2028 window). Neither major cost-seg shop covers it yet. If you own manufacturing-adjacent real property, ask about it by name.

What to do with this, this week

  • Locate your contract date for anything bought, built, or renovated since late 2024. It’s in your file — you probably didn’t know it was a tax document.
  • If you’re under contract now, the binding-contract date of your purchase agreement generally governs — sequence closings and entity transfers accordingly (get advice before assigning contracts across an LLC swap; that’s a classic self-inflicted wound).
  • Treat the 100% window as permanent but acquisition-date-limited: waiting doesn’t reduce your rate, it just delays the deduction. The reason to move on your study is cash-flow timing — every year of regular-MACRS waiting is a year of 100% you’ll never get back on the same dollars.

Sources above are primary law and the IRS’s own interim guidance. When a competing explanation conflicts with the statute PDF, the statute wins — including when the competing explanation is ours.