Definition
CPA, or Cost Per Action, is a commission model where you pay your affiliate partner a fixed dollar amount every time they drive a specific action. That action is usually a sale, but it can also be a signup, a free trial, a form submission, or any conversion event you define. Unlike impression-based or click-based models, you only pay when something measurable happens.
How it works
Say you run a SaaS product with a $50/month plan. You set a CPA of $30 for every new paying customer an affiliate sends you. An affiliate writes a review, includes their tracking link, and a reader clicks through and subscribes. Your tracking system fires a postback to confirm the conversion, and the affiliate earns $30. If nobody converts, you pay nothing.
CPA is often compared to CPC (cost per click) and CPM (cost per thousand impressions). The difference is risk. With CPC, you pay for clicks whether or not they convert. With CPM, you pay for eyeballs. With CPA, the affiliate absorbs the traffic risk and you only pay for results.
Why it matters
CPA gives you predictable unit economics. You know exactly what each customer acquisition costs before it happens, which makes budgeting straightforward. It also aligns incentives: affiliates are motivated to send qualified traffic because junk clicks earn them nothing. The tradeoff is that top affiliates may prefer revenue share for high-LTV products, since a flat payout caps their upside.
For program managers, the key decision is setting the right CPA. Too low and quality partners ignore you. Too high and your margins disappear. Look at your customer lifetime value, subtract your target margin, and work backward to a CPA that makes both sides profitable.
Trcker tip
Trcker lets you set different CPA rates per partner or tier, so you can reward your top performers without overpaying on new affiliates who haven't proven their traffic quality yet.