A screen answers one question: is a full study likely to be worth it? It is a modeled estimate built from your purchase price, property type, land allocation, and placed-in-service date, producing an expected reclassification range and a projected first-year deduction. A full engineering-based study is the documented analysis that actually supports the allocations on your tax return.
What a screen does
A screen runs in minutes and costs little or nothing. Amadae's savings playbook includes a cost segregation screen that estimates the reclassification and first-year benefit for a property, and its free Tax Strategy Projector calculator models the combined short-term rental plus cost segregation strategy before you spend anything. A screen is explicitly not an engineering study: no site data, no component takeoffs, no audit deliverable. Its job is feasibility, sizing, and sequencing, deciding whether the projected benefit clears the study fee and whether you can even use the loss under IRC section 469.
What a full study adds
The IRS Cost Segregation Audit Techniques Guide does not prescribe a required format, but it is blunt that reliability tracks methodology: studies built on engineering takeoffs, construction documents, photographs, and component-level cost data are the most defensible, while rule-of-thumb percentage allocations are the least. The full study delivers the asset-by-asset detail your preparer books into the depreciation schedule and the documentation that answers an examiner's questions years later. If a look-back is involved, the study also supplies the numbers behind the Form 3115 section 481(a) catch-up.
A worked example
You are weighing a study on a $1,150,000 short-term rental acquired in May 2026. A screen using a 20% land allocation projects a 25% to 30% reclassification, roughly $230,000 to $275,000 of basis moving into 5- and 15-year property, all bonus-eligible at 100% under IRC section 168(k) because the acquisition came after January 19, 2025. Against a study fee in the low four figures, the screen says proceed. The engineering study then replaces the range with a documented number, say $256,400, and that is what goes on the return.
When each is enough
A screen is enough for deciding whether to engage, projecting quarterly estimates, comparing candidate properties, and modeling scenarios. It is never enough to claim the allocations on a filed return; self-made percentages invite the 20% accuracy-related penalty under IRC section 6662 if an overstated allocation produces an underpayment. Conversely, skipping the screen and buying studies on autopilot wastes money on properties with high land value, small basis, or losses you cannot deduct this year. Screen first, study second, file third.