How to calculate CPA from ad spend and conversions
Cost per acquisition divides advertising spend by the number of attributed conversions or orders. Define the conversion consistently: a lead CPA, new-customer CPA, and order CPA are not interchangeable.
The calculator compares current CPA with average order value multiplied by contribution margin. That second number is a simplified break-even CPA before lifetime value and fixed overhead.
CPA = advertising spend ÷ attributed conversionsCost per acquisition worked example from ad spend and conversions
$2,400 of ad spend divided by 80 attributed orders produces a $30 order CPA. If AOV is $75 and contribution margin before ads is 45%, the simplified first-order CPA ceiling is $33.75, leaving $3.75 of estimated contribution per attributed order at the observed CPA.
The answer changes with the denominator. If only 60 of those 80 orders came from new customers, new-customer CPA is $40 rather than $30. Label the conversion event before comparing campaigns or using the result in a budget decision.
How to interpret current CPA vs maximum CPA
Maximum break-even CPA equals AOV multiplied by the contribution margin available before advertising. At a target ROAS, planned CPA can also be estimated as AOV divided by target ROAS. Both approaches should agree when margin and target are based on the same order economics.
CPA vs CAC vs cost per conversion
CPA is a flexible advertising metric whose acquisition event may be a lead, order, signup, or customer. Cost per conversion is similarly event-based. CAC should represent the cost to acquire a new customer and may include sales, creative, agency, or other acquisition expenses beyond platform media spend.
Do not compare the labels until spend scope and conversion scope match. A platform purchase CPA can be useful for campaign control while a fully loaded new-customer CAC is the stronger business metric for payback and customer economics.
CPA and maximum CPA calculator FAQ
Should I use purchases or new customers?
Use the denominator that matches the business question. New-customer CPA is usually more useful for acquisition planning, while order CPA includes repeat orders unless filtered.
Does maximum CPA include customer lifetime value?
No. This calculator uses first-order AOV and contribution margin. Add lifetime value only when repeat-purchase data and payback timing are validated.