The maximum daily ad budget a product can spend without going net-negative:
Max daily budget = Break-even TACoS × average daily sales revenue (trailing 30 days)
Break-even TACoS is the product's margin percentage after COGS, shipping, returns, FBA fee, and seller fee — the money left over before ads are paid for. Multiplying that margin by trailing revenue converts "how much profit exists" into "how much could be spent on ads before profit hits zero."
Because break-even TACoS is mathematically equal to product margin, this ceiling is really just "spend 100% of your margin on ads" — framed as a deliberate zero-profit growth strategy for aggressive volume/rank pursuit, not a miscalculation.
Distinct from TACoS-Based Ad Budget Formula (Existing Products) (a target budget for steady-state operation): this is a hard ceiling check, used to sanity-check that a target budget doesn't exceed what margin allows.