CPA Calculator
Cost per acquisition in any direction, with the counting model explicit, and the number that actually matters derived from your margin: the CPA you can afford, and the max CPC it implies.
CPA solver enter any two, the third is solved
Full funnel
Unit economics: contribution and break-even bids
Scenario planner arithmetic from your assumptions, not a forecast
Show the math
The affordable CPA is a business number, not an ad number
Ad platforms will happily optimize toward whatever CPA target you type in; whether that target loses money is your problem. The affordable ceiling comes from order economics: what an average order contributes after product and per-order costs. This page derives break-even CPA from those inputs, connects it to a max CPC through your acquisition rate, and keeps the ROAS view beside it with break-even ROAS from the same margin. One set of economics, every bidding ceiling, consistently.
CPA, the formula and a worked example
Cost per acquisition (CPA) is what one conversion costs you in media spend: total spend divided by the number of conversions in the same period. If a campaign spent 1,200 and produced 40 orders, the CPA is 30. The counting model matters more than the arithmetic: a conversion can be an order, a lead, a trial or a call, and a CPA quoted without saying which one is not comparable to anything.
The break-even CPA is the number the ad platform cannot tell you. Take the average order value, subtract product cost and the per-order costs (payment fees, packaging, shipping you absorb) and what is left is the contribution per order. A CPA above that loses money on the first purchase, whatever the dashboard calls it. With a 90 order value and 55 in costs the ceiling is 35; the campaign above, at 30, is inside it with 5 of headroom per order.
CPA misleads in three common cases. Attribution windows: a 7-day click window and a 30-day view window produce different conversion counts for the same spend, so the same campaign has two CPAs. Delayed conversions: a lead-gen campaign looks expensive for the first week because the conversions have not landed yet. Blended versus incremental: a branded search campaign reports a wonderful CPA on orders that would have happened anyway. Compare CPAs only inside one counting model and one window.
CPA FAQ
How is CPA calculated?
CPA = ad spend / conversions. $900 producing 38 acquisitions is a $23.68 CPA. The solver above runs all three directions: conversions a budget must produce to hit a target CPA, or the spend a conversion goal allows. The counting model matters: this page distinguishes unique acquisitions (real customers or leads) from all conversion actions, because platforms can count several actions per click.
What CPA can I afford?
Break-even CPA = average order value x contribution margin - fixed per-order costs. A $100 order at a 40% margin with $5 of per-order fixed costs affords a $35 CPA at break-even; pay more and each acquisition loses money on first-order economics. Enter those three numbers in the unit economics panel and the calculator derives it, plus the max CPC your acquisition rate implies.
How do CPA and max CPC connect?
Through the acquisition rate: max CPC = affordable CPA x acquisition rate. If you can pay $35 per acquisition and 4% of clicks acquire, each click is worth at most $1.40. The calculator computes this from your funnel’s actual rate when it is valid, with the caveat printed: auctions vary actual CPCs and rates drift, so treat it as a ceiling, not a bid.
Should I judge campaigns on CPA or ROAS?
They fail differently. CPA ignores order value: a $30 CPA is great for $200 orders and ruinous for $40 ones. ROAS ignores costs: a 3x ROAS loses money below a 33% margin. The pair, anchored to your contribution margin (break-even ROAS = 1/margin), covers both failure modes; this page computes all of it from one set of inputs.
More free tools: Ad Metrics Calculator · CPM Calculator · ROAS Calculator · Break-Even Calculator