ROAS explained: the number every ad platform shows, and the one it doesn't

Return on ad spend is the headline metric of every ad platform, and a 3× ROAS gets celebrated in a lot of meetings where it shouldn't. The number is simple; what it leaves out is the margin, the returns, and the customers who would have bought anyway. This guide explains ROAS, the break-even figure you need next to it, and how the other campaign metrics connect — the arithmetic that the ad cost calculator does from any dashboard's figures.

What ROAS is

ROAS = revenue attributed to the ads ÷ ad spend. Spend £1,000, get £3,000 of tracked sales, ROAS is 3× (sometimes written 300%). It is a ratio of revenue, not profit, which is the whole problem: revenue includes the cost of the goods, the payment fees, the shipping you paid, and the returns that haven't arrived yet. ROAS tells you the ads generated sales; it doesn't tell you whether you made money.

Break-even ROAS: the number that matters

Only the margin on revenue is available to pay for ads. If your gross margin is 40%, each £1 of revenue leaves £0.40 after the cost of goods, so ads break even when spend equals 40% of attributed revenue — a ROAS of 1 ÷ 0.40 = 2.5×. At 25% margin, break-even is 4×; at 60%, 1.67×. The honest campaign result is the gap between actual ROAS and break-even, expressed as profit after ad spend: revenue × margin − spend. A 3× ROAS at a 25% margin is a £250 loss on every £1,000 spent. Use contribution margin (after variable costs like fees and shipping), not the headline gross margin, and it gets stricter. How to calculate your break-even point (and what it doesn't tell you) covers where margin comes from.

The metric chain: CPM to CPC to CPA

Every campaign is a funnel with a price at each step. CPM (cost per thousand impressions) is what the auction charges to be seen; CTR (clicks ÷ impressions) is how often the ad earns a click; together they set CPC (cost per click). Conversion rate (conversions ÷ clicks) is what the landing page does with the click; with CPC it sets CPA (cost per acquisition). Average order value times margin, compared with CPA, is profit per customer. The chain diagnoses problems: a good CTR with a bad conversion rate is a landing-page problem, not an ad problem; a low CPC with poor conversions often means the ad attracts the wrong people. Cheap clicks are not the goal; profitable customers are.

Why the dashboard flatters you

Platform-reported conversions are claimed under attribution windows — a purchase within 7 days of a click, or within 1 day of a view, counts — and different platforms claim the same sale, so adding their ROAS figures overstates the truth. Some attributed buyers would have bought anyway (brand searches, returning customers), which is why the gold standard is an incrementality test: hold out a region or audience and measure the lift. Returns, chargebacks and cancelled subscriptions arrive after the dashboard has declared victory. None of this makes ROAS useless — it's the best day-to-day signal — but it means the break-even threshold should sit above the arithmetic minimum, and campaigns should be judged on the platform where they run and against blended, business-level numbers over months.

Setting targets that mean something

Set a target ROAS from the margin, not from a benchmark: break-even plus the profit you need. Know your CPA ceiling — the most you can pay for a customer and still profit, which for subscription or repeat businesses includes lifetime value, not the first order. Decide the reporting window and stick to it. And keep the tests honest: when a new creative "beats" the old one, the A/B test calculator will tell you whether the difference is real. The margin calculator and the UTM builder supply the inputs.