Ad math calculators
These four calculators use your own price, costs and conversions to find the point where ads stop losing money: gross margin sets what you can spend, break-even ROAS and max CPA tell you when to stop, and conversion rate tells you whether the problem is the page or the budget.
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| Calculator | Answers | Formula |
|---|---|---|
| Gross margin calculator | What each sale leaves you, and how margin differs from markup | Gross margin = gross profit ÷ price × 100% |
| Break-even ROAS calculator | The ROAS your ads must beat to stop losing money | Break-even ROAS = order value ÷ contribution per order |
| Max CPA calculator | The most one order, and one click, can cost in ads | Break-even CPA = order value − variable cost per order |
| Conversion rate calculator | Your rate, whether the sample is big enough, and visitors needed | Conversion rate = conversions ÷ visitors × 100% |
One order, worked through all four
The same order through all four calculators: order value 1,200, goods 480, shipping, payment fees and packing 240 together, a profit of 10% of the order kept back, and a 2% conversion rate on the product page.
| Number | Working | Result | Calculator |
|---|---|---|---|
| Contribution per order | 1,200 − 480 − 240 | 480 | Break-even ROAS calculator |
| Contribution margin | 480 ÷ 1,200 | 40% | Gross margin calculator |
| Break-even ROAS | 1,200 ÷ 480 | 2.50 | Break-even ROAS calculator |
| Break-even CPA | = contribution per order | 480 | Max CPA calculator |
| Target CPA | 480 − 1,200 × 10% | 360 | Max CPA calculator |
| Target ROAS | 1,200 ÷ 360 | 3.33 | Max CPA calculator |
| Affordable CPC | 360 × 2% | 7.2 | Max CPA calculator |
| Visits for 10 orders a day | 10 ÷ 2% | 500 | Conversion rate calculator |
If this business reports a ROAS of 3, it is making money but is short of its 3.33 target; at 2.2 every extra sale loses a little more. In the accounts we handle, we fill in this table first, then decide whether to add budget, change creative or fix the page: low ROAS with a normal conversion rate usually points at creative or audience; if conversion drops to 1%, the affordable CPC halves to 3.6, so fix the page before talking budget.
Which to work out first
Suggested order: gross margin first, then break-even ROAS with shipping and fees added, then max CPA, then conversion rate to check the page.
FAQ
Margin or markup: which one sets the ad threshold?
Margin, and more precisely contribution margin after shipping, payment fees and packing. Markup divides by cost, so a break-even ROAS worked out from it comes out too low and losing orders look profitable.
Should I watch ROAS or CPA?
When orders are all about the same value, CPA is enough. When order values vary a lot (add-ons, bundles), watch ROAS, because it accounts for each order bringing in different revenue. Both thresholds come from the same contribution, so they never disagree.
Does break-even ROAS include rent and salaries?
No. It covers the variable cost of each order only: goods, shipping, payment fees, packing. Check fixed costs separately with the month’s total revenue divided by total ad spend (MER).
Are the numbers I type recorded?
No. The calculation runs in your browser; the page does not send or store what you type or put it in the URL.
Sources
- AccountingTools: Gross margin · checked 2026-10-23
- AccountingTools: Contribution margin · checked 2026-10-23
- Meta 企業商家使用說明: 購買 ROAS · checked 2026-10-23
- Google Ads Help: About Target CPA bidding · checked 2026-10-23
- Google Ads Help: Conversion rate: Definition · checked 2026-10-23
Work out your stop, target and scale lines from your own numbers.
Intermediate, chapter 5 puts shipping, free-shipping offers, payment fees, returns and payment success into cost, and builds the cost sheet in Google Sheets. Read online, one-time purchase; the opening chapters of each level are free.