The highest-value window is the tax year the property is placed in service, with the study delivered before you file that year's return, extensions included. That timing puts the entire reclassified amount, at 100% bonus under IRC section 168(k) for property acquired after January 19, 2025, against the first year's income with no procedural overhead.
The four windows, ranked
1. The year placed in service. The study simply sets the opening depreciation schedule. You do not need it by December 31; you need it before filing, so a property placed in service in November can be studied in February and still land on that first return.
2. After a major renovation. New construction and improvements create fresh basis, much of it bonus-eligible. Studying immediately after completion also captures the documentation for a partial asset disposition on what you ripped out.
3. A look-back on property owned for years. Missed acceleration is not lost. A study on a property placed in service in a prior year is claimed through Form 3115 as an automatic accounting method change, with the entire shortfall deducted in the current year as a section 481(a) adjustment per the Form 3115 instructions. No amended returns. Note the bonus rate is frozen by the original acquisition and placed-in-service dates, so a 2024 placement catches up at 60%, not today's 100%.
4. The wrong time. A year when you cannot use the loss. If IRC section 469 will suspend the deduction because you lack real estate professional status, short-term rental material participation, or passive income, consider deferring the study, or electing out of bonus by class under section 168(k)(7), so the deduction lands in a high-income year.
A worked example
Two investors in 2026. The first buys an $850,000 short-term rental in August 2026, runs a screen in the fall, commissions the study in January 2027, and files the 2026 return with roughly $190,000 of bonus depreciation from a 28% reclassification. The second has owned a $700,000 fourplex since 2021, depreciating it straight-line. A 2026 study plus Form 3115 computes about 5 years of missed acceleration as a single section 481(a) deduction on the 2026 return, at the bonus rate that applied to the 2021 placement.
How to sequence it
Screen before you commission anything. Amadae's savings playbook includes a cost segregation screen that models the benefit, its property tracking tab keeps in-service dates straight, and the platform prepares the Form 3115 catch-up and files the return that uses the study. The one deadline that is truly hard: the study's results must land on a filed return or a filed Form 3115. Everything before that is flexible.