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CPA Calculator
Cost per acquisition is spend divided by conversions. Add your order value and contribution margin and the page works out the CPA at which you stop making money.
Your numbers
Purchases, signups or booked calls. Keep it the same action you are optimising the campaign for.
The share of the order left after EVERY variable cost: goods, shipping, payment fees. Not gross margin, which leaves shipping in and quietly raises the CPA the page tells you that you can afford.
Your cost per acquisition
CPA
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Break-even CPA
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Profit per conversion
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The formulas
CPA = ad spend / conversions
Break-even CPA = order value x contribution margin
Shares the numbers you entered, not your data. Everything is in the link itself.
What is CPA?
CPA is cost per acquisition: what you paid, on average, for each conversion. Whether a conversion is a purchase, a signup or a booked call is your decision, and the only rule is that it stays the same action on both sides of the division.
On its own a CPA is arithmetic without a verdict. A $25 CPA is excellent against a $90 order and fatal against a $30 one, which is why this page asks for two more numbers.
CPA = ad spend / conversions
A worked example
A campaign spends $4,000 and produces 160 conversions on a $90 average order at a 40% contribution margin.
CPA = $4,000 / 160 = $25.00
Break-even CPA = $90 x 0.40 = $36.00
Profit per conversion = $36.00 - $25.00 = $11.00
Start from the break-even CPA
Your break-even CPA is the contribution margin on an average order: the most you can pay to win a customer before the campaign starts costing you money. Contribution margin, not gross margin, and the difference is not pedantry: gross margin leaves shipping and payment fees in, so using it tells you that you can afford a CPA you cannot. Above it you are buying revenue, below it you are buying profit.
Run the same campaign against a $50 order at the same 40% contribution margin and the break-even drops to $20.00. The CPA has not moved, and every conversion now loses $5.00. The number that changed was never in the ad account.
If you would rather work this from the revenue side, the ROAS calculator takes the same idea as a multiple. To see what a conversion is worth over its lifetime, use the CLV calculator.
Reading a CPA honestly
Count the costs beyond media
Creator fees, agency retainers and production all bought those conversions. A CPA that counts only ad spend is a number for reassurance, not for decisions.
Match the window to the purchase
A considered purchase attributed on a one-day window will always look expensive. Pick the window from how people actually buy, then keep it fixed.
Watch the mix behind the average
A blended CPA hides one audience subsidising another. Split it before you scale anything.
Lifetime value changes the ceiling
If customers come back, break-even on the first order is the wrong bar. That is what the CLV calculator is for.
Use this calculator on your own site
Free to embed and free to cite, no attribution deal needed. Writers, agencies and course authors are welcome to drop the calculator straight into a post, and a credit link back is all we ask.
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Frequently Asked Questions
What is CPA?
CPA is cost per acquisition: total ad spend divided by the number of conversions it produced. A campaign spending $4,000 for 160 conversions has a CPA of $25.00. The conversion can be a purchase, a signup or a lead, as long as it is the same action you are optimising for.
How do I calculate CPA?
Divide total spend by total conversions. $4,000 across 160 conversions is $25.00 each. Add your average order value and contribution margin above and the calculator also returns your break-even CPA and the profit on every conversion.
What is a good CPA?
Any CPA below your break-even CPA, which is your average order value multiplied by your contribution margin: the share of the order left after goods, shipping and payment fees. At a $90 order and a 40% contribution margin, break-even is $36.00, so a $25.00 CPA earns $11.00 per conversion. There is no useful industry benchmark, because the same CPA is excellent for one business and fatal for another.
What is the difference between CPA and CAC?
CPA usually measures the cost of one conversion inside a campaign, counting media spend. CAC measures the cost of winning a customer across the whole business, and includes sales salaries, tooling and agency fees as well. CPA is the campaign question, CAC is the company one.
Should I count creator and agency fees in my CPA?
Yes, if you want the number to inform a decision. Everything you paid to produce and place the ads bought those conversions. A media-only CPA is fine for comparing two ad sets against each other and misleading for deciding whether the channel works.
Do I need an account?
No account, no email, no credit card. Nothing you type is sent anywhere: the arithmetic runs in your browser.
A lower CPA usually starts with a better ad
Once the targeting is sensible, the creative is what moves cost per acquisition. Selzee reads your reviews, comments and campaign results, finds the angles and objections your customers keep raising, and turns them into the next round of briefs and ads.
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