Amazon Sponsored Products charge per click, and the standard way to judge them is ACoS — advertising cost of sales, ad spend ÷ sales generated by ads. The number that makes ACoS meaningful is your break-even ACoS: the ACoS at which an advertised unit makes exactly zero profit. It comes straight from your margin before ads, which the Amazon FBA calculator gives you.
Three definitions
- ACoS = ad spend ÷ ad-attributed sales. A $10 spend that produced $50 of sales is 20% ACoS.
- ROAS = ad-attributed sales ÷ ad spend = 1 ÷ ACoS. 20% ACoS is 5× ROAS.
- TACoS = ad spend ÷ total sales (organic + ads). If the same $10 sits alongside $100 of total sales, TACoS is 10%.
ACoS tells you whether a campaign pays for itself. TACoS tells you what advertising costs the business as a whole, and it is what belongs in the pricing formula.
Break-even ACoS = margin before ads
If a unit nets $6 on a $30 price before any advertising, you can spend up to $6 of ads to sell it and still break even — $6 ÷ $30 = 20% break-even ACoS. In general:
Break-even ACoS = (price − all fees − all costs) ÷ price = pre-ad margin
Two consequences follow. A higher pre-ad margin gives you more room to bid; and anything that raises fees — a heavier package, a peak-season table, a price drop that crosses into a lower referral tier the wrong way — cuts your ad room by the same amount.
Target ACoS
Break-even is the ceiling, not the goal. Decide how much margin you want to keep on advertised sales and subtract it:
Target ACoS = break-even ACoS − margin you want to keep on ad sales
With 20% break-even and a wish to keep 8% on advertised units, target ACoS is 12%. Many sellers run at or above break-even during a launch and tighten to target once organic sales carry the listing; the important thing is that the choice is deliberate.
Worked example with 2026 FBA fees
Small standard item, 12 oz, Home & Kitchen, $30 price, product cost $9, inbound $0.80, one month of storage.
| Line | Amount |
|---|---|
| Price | $30.00 |
| Referral fee 15% | −$4.50 |
| FBA fee 10–12 oz, $10–50 band, incl. 3.5% surcharge | −$3.91 |
| Storage ≈ 0.07 cu ft × $0.78 | −$0.05 |
| Product cost + inbound | −$9.80 |
| Profit before ads | $11.74 (39.1%) |
- Break-even ACoS: 39%. Up to $11.74 of ad spend per advertised unit is neutral.
- Target ACoS at 15% kept margin: 24%, or about $7.20 of ads per advertised unit.
- If the same item is sold at $24.99 the pre-ad margin falls to about 30% (the fees are mostly fixed), and the target ACoS at the same kept margin becomes 15%.
From ACoS to a maximum bid
Cost per click × clicks per sale = ad cost per sale. With a conversion rate c (orders ÷ clicks):
Max CPC = target ACoS × price × c
At 24% target ACoS, $30 price and a 10% conversion rate: 0.24 × 30 × 0.10 = $0.72 per click. If conversion is 5%, the ceiling halves to $0.36 — which is why improving the listing (images, reviews, price) does more for PPC than bidding tactics. Amazon’s suggested bids are guesses about competition, not about your profit; compute your own ceiling and bid below it.
Reading the numbers correctly
- Attribution window. Amazon attributes sales up to 7 days after the click for Sponsored Products (14 days for brand campaigns), so ACoS for the last few days is always overstated. Judge on a 14–30-day window.
- Halo sales. A click on one variation that leads to a sale of another is still counted; genuine organic lift from higher rank is not. TACoS captures the second effect; ACoS does not.
- Peak season. From October 15 the FBA fee rises by $0.19–0.54 per unit for standard sizes, while CPCs rise with competition. Recompute break-even before Q4.
- Coupons and deals reduce the price in the denominator and the margin in the numerator at once; a 10% coupon on the example above drops break-even ACoS from 39% to about 34%.
Get your product’s pre-ad margin from the Amazon FBA calculator — with the PPC field left at zero — and set your target ACoS from that number rather than from an industry average.