Marketing
How do you calculate cost per acquisition (CPA)?
Cost per acquisition from ad spend and conversions — or the budget you need for your target CPA.
Quick answer
CPA — cost per acquisition — is the number that tells you whether paid traffic is buying customers profitably. It is simply ad spend divided by conversions, but the definition of "conversion" must match your business: a sale, a qualified lead, or a signup worth different amounts.
Cost per acquisition (CPA)
$25.00
- Per conversion
- $25.00
CPA = spend ÷ conversions. Compare it to customer lifetime value — if CPA is half your margin per sale, the campaign is healthy. Track the same conversion definition your ad platform uses.
How it works
Healthy CPA is usually well below your gross profit per customer, and ideally below half of customer lifetime value if you can afford multiple purchases to break even. The calculator above gives actual CPA from your campaign data, or the budget you need for a target CPA. Before scaling spend, sanity-check against margins — a Google Ads or Meta Ads reference book helps structure tests, but the math here is what decides if those tests can ever win.
Before optimising a CPA, check that the conversions in the numerator are real. Every platform grades its own homework and counts under its own attribution window, so the same purchase can be claimed by search, by social and by the affiliate network at once — add up what the dashboards report and the total routinely exceeds the orders actually in your back office. The check takes five minutes: compare the sum of platform-reported conversions against your real order count for the same period. If they diverge, the individual CPAs are all flattered, and comparing one channel's CPA to another's is comparing two different accounting conventions.
Frequently asked questions
What is a good CPA for Facebook or Google Ads?+
There is no universal number — it depends on your average order value and margin. If you sell a €80 product with €40 gross margin, a €20 CPA leaves room; a €60 CPA probably does not. Benchmark against your own unit economics, not industry blog posts.
CPA vs CPC — what is the difference?+
CPC is cost per click; CPA is cost per conversion. You might pay €0.40 per click but €25 per purchase if only 1.6% of clicks convert. Optimize the full funnel — landing page, offer, checkout — not just the ad click price.
Should I optimize for CPA or ROAS?+
ROAS (return on ad spend) is better when order values vary a lot — it ties spend directly to revenue. CPA is cleaner when conversions have similar value (leads, subscriptions at fixed price). Many platforms let you target either; pick the metric that matches how you judge success.
Why does my platform CPA differ from this calculator?+
Attribution windows, view-through conversions, delayed purchases and duplicate counting all change platform-reported CPA. Use this calculator for simple spend ÷ conversions sanity checks; reconcile with your CRM or shop backend for the truth.
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