They are two different documents with two different jobs. A cost segregation study is a point-in-time engineering analysis: it examines one property, allocates its cost basis across MACRS classes, and delivers a report. A depreciation schedule is the living, asset-by-asset ledger your tax preparer maintains for every depreciable asset you own, updated every year and summarized on Form 4562 with your return.
What each one contains
The study, built to the standards described in the IRS Cost Segregation Audit Techniques Guide, documents methodology, component takeoffs, photographs, cost source data, and a final allocation: so much basis to 5-year property, so much to 7-year, 15-year, and the 27.5- or 39-year remainder. It is evidence. It does not calculate your deduction for any particular year.
The depreciation schedule turns that allocation into numbers on a return. Each segregated group becomes one or more line items with its own in-service date, method, convention, prior accumulated depreciation, and current-year deduction. The schedule is also where everything after the study lives: later renovations add lines, partial asset dispositions remove them, and bonus elections under IRC section 168(k) are tracked class by class.
A worked example
You commission a study on a $900,000 fourplex with $180,000 allocated to land. The report allocates $110,000 to 5-year property, $70,000 to 15-year land improvements, and $540,000 to 27.5-year residential rental property. Your preparer books 3 asset groups on the schedule. In year 1 the schedule shows $180,000 of bonus depreciation on the short-life groups, at 100% for property acquired after January 19, 2025 under section 168(k), plus the first slice of 27.5-year straight-line on the building. In year 7, when you replace the original carpet, the schedule, not the study, is what tells you the remaining basis you can write off.
Why the distinction matters
A study that never makes it into the schedule changes nothing. The IRS sees your depreciation through Form 4562 and the schedule behind it, so the study only has effect when its allocations are booked and filed. The reverse is also true: if the study arrives after you have already filed one or more returns using the default 27.5- or 39-year life, your preparer cannot quietly swap the schedule. That is a change in accounting method requiring Form 3115 and a section 481(a) catch-up adjustment per the Form 3115 instructions.
Amadae sits on the schedule side of this divide: it maintains MACRS depreciation schedules, screens properties for cost segregation potential inside its savings playbook, coordinates the engineering study with a study firm, computes the Form 3115 catch-up when a look-back applies, and files the return. The engineering study itself always comes from an engineering-based provider.