For a product with sales history, the monthly ad budget is derived from a target TACoS rather than picked arbitrarily:
"Total Revenue" is ad + organic revenue combined — the TACoS denominator. Anchoring on TACoS and total revenue (rather than ACoS and ad revenue alone) makes this a top-down, whole-business budget target instead of one derived from individual campaign guesses.
Feeds into a Campaign Planner (Pre-Launch Budget Worksheet), where the resulting daily figure is checked against the sum of individual campaign budgets before any campaign is created.
Contrast with Break-Even TACoS Budget Ceiling, which computes a maximum sane budget (a ceiling on margin) rather than a target; and with New-Launch Ad Budget Formula (CPC ÷ CVR × Target Sales), used only when no sales history exists yet to compute a TACoS.