Break-Even ACOS: What It Is and How to Calculate It

Ask "what is a good ACOS?" in any seller forum and you will get numbers from 15% to 60% — all of them meaningless without your margin. ACOS is only interpretable against your break-even, and that number takes thirty seconds to calculate.

The formula

Break-even ACOS = pre-ad profit ÷ selling price. Take your price, subtract all marketplace fees and product costs (before any ad spend), and divide by price. A $29.99 product that nets $12.79 before ads has a break-even ACOS of 42.6%. Spend more than 42.6 cents in ads per dollar of ad revenue, and each advertised sale loses money.

Target ACOS: the number you actually manage to

Break-even is a cliff edge, not a goal. Decide the net margin you want to keep — say 10% — and subtract it: target ACOS = break-even − desired net margin = 32.6%. Manage campaigns to target, tolerate break-even during launches when you are deliberately buying rank and reviews.

From ACOS to a real bid

Max CPC = price × target ACOS × conversion rate. At a 10% conversion rate, that $29.99 product supports bids up to $29.99 × 0.326 × 0.10 ≈ $0.98. If a keyword needs $2.50 clicks to appear, you now know precisely how unprofitable it is — or how much conversion rate must improve to afford it.

ACOS vs TACOS

ACOS measures spend against ad-attributed revenue; TACOS divides spend by total revenue, capturing the organic halo that advertising creates. Mature products should show TACOS drifting down over time while total sales grow — if TACOS climbs while sales stay flat, ads are replacing organic sales, not adding to them. Your margins upstream of ads are set by fees — check the 2026 FBA fee breakdown to make sure the margin you are protecting is real.