Guides · 6 in-depth articles
The mechanics behind the math.
Six guides on how Form 3115 §481(a) catch-up depreciation actually works, written by the Cost Seg Smart engineering team. Each guide focuses on one piece — file, compute, decide, prove, plan.
01 · FILING
Form 3115 for Cost Segregation: A Step-by-Step Filing Guide
DCN 7, required attachments, where to mail, the 5 mistakes that get filings rejected. The how-to.
02 · MATH
§481(a) Adjustment: How Catch-Up Depreciation Actually Works
The math, formally. Worked $500K Phoenix duplex example showing every line of the §481(a) computation.
03 · DECISION
Form 3115 vs. Amended Returns: Which Should You Use?
Side-by-side. When 3115 wins, when 1040X is the only path, and the one scenario where they tie.
04 · PROOF
Catch-Up Depreciation Examples: 5 Real Properties, 5 Tax Outcomes
Phoenix duplex, Nashville STR, Austin office, suburban SFR, Sedona STR — full math on each.
05 · LIMITS
How Far Back Can You Catch Up Missed Depreciation?
Form 3115 has no statute-of-limitations cap. The 3-year rule everyone repeats only applies to amended returns.
06 · STR
Catch-Up Depreciation for Short-Term Rentals: The STR Lookback Strategy
Why STRs win. §469(c)(7) STR exception, material participation, $750K Nashville cabin walked through.
Ready to see your number?
The homepage calculator returns a Year-1 catch-up estimate in 30 seconds — no email required.
Run the calculator Order a lookback study