Break-Even ROAS and CPA: How Much Can You Spend on Ads?

By Raúl Vaquerizo Tortosa · Published October 26, 2026

“Is a ROAS of 3 good?” has no general answer. A return on ad spend of 3 can be very profitable for one store and lose money for another. What matters is your break-even point, and that comes from your own margins, not from benchmarks.

Start with contribution before ads

For one order, take the net revenue (excluding sales tax or VAT) and subtract every cost that the order causes, except advertising:

• product cost (ideally landed cost)
• shipping and packaging
• payment and platform fees
• expected returns and refunds
• any other per-order cost

What is left is the contribution before ads - the most an order can give back before it covers fixed costs.

The three numbers

Break-even CPA = contribution before ads

Break-even ROAS = net revenue ÷ contribution before ads

Target ROAS for a profit margin m = net revenue ÷ (contribution before ads − m × net revenue)

The first tells you the most you can pay to acquire an order. The second expresses the same limit as the ratio ad platforms report. The third tells you the ROAS you need to keep a chosen profit margin after advertising.

A worked example

An illustrative order:

• Break-even CPA: $28.90. Pay more than that to win an order and the order loses money.
• Break-even ROAS: $60.00 ÷ $28.90 ≈ 2.08. Every $1 of ad spend must bring in at least about $2.08 of net revenue.
• Target ROAS for a 10% profit margin: you want $6.00 (10% of $60) left after ads, so ads can take $28.90 − $6.00 = $22.90. Target ROAS = $60.00 ÷ $22.90 ≈ 2.62.

You can get these numbers for your own products from the Shopify profit margin calculator, which shows break-even CPA and ROAS alongside contribution profit.

Amazon: ACoS

On Amazon, advertising performance is usually shown as ACoS (advertising cost of sale), which is ad spend divided by ad-attributed sales - the inverse of ROAS:

ACoS = 1 ÷ ROAS, and break-even ACoS = contribution before ads ÷ net revenue

In the example, break-even ACoS would be $28.90 ÷ $60.00 ≈ 48.2%. On Amazon, the costs to subtract include the referral fee and FBA fees; the Amazon FBA calculator gives you the per-unit profit before advertising if you set advertising to zero.

Things that distort ROAS

• Revenue definitions. Ad platforms often count revenue including tax and shipping. If so, convert your break-even ROAS to the same basis, or you will set targets that are too easy.
• Attribution. Platforms may take credit for sales that would have happened anyway, or miss some they caused. Compare platform-reported ROAS with your actual sales and total ad spend (sometimes called blended or marketing efficiency ratio).
• Discounts. A discount code used with an ad lowers revenue and contribution for that order, which raises your break-even ROAS.
• Returns. If returns are higher for ad-driven orders, include that in the returns allowance.

What about repeat customers?

The calculations above assume each order must pay for its own advertising. If customers reliably come back, you might accept a higher acquisition cost on the first order and recover it from later ones. That can be a sound strategy, but it depends on repeat-purchase rates and margins you have actually measured in your own data. Until you have that data, a first-order break-even is the safer limit.

A simple routine

1. Calculate contribution before ads for your main products.
2. Set break-even and target ROAS (or ACoS) per product or product group.
3. Compare campaign results with those targets, using revenue on the same basis.
4. Recalculate whenever costs change: new supplier prices, carrier rates or fees all move the break-even point.