CPA indicates how much one completed conversion cost. Once you have a handle on CPA, you can decide which campaigns to continue, which to cut, and where to invest more.
What is CPA?
CPA (Cost Per Action / Acquisition) is the cost of a completed conversion. It measures how much one desired action cost – such as a purchase, order, reservation, or demo, not just a lead.
In short: CPA = Cost / Completed conversions.
How to calculate CPA (example)
Media cost: €3,600
Completed conversions (purchases/reservations etc.): 120 pcs
CPA = 3,600 / 120 = €30
If you are measuring leads, it is better to use CPL. CPA is most effective when the goal is “final” (purchase, contract, order).
7 steps to implementation
Define the “action”. What is a completed conversion? Purchase, order, reservation? Write it out.
Connect values. For GA4: conversion event + value (if available), so you can also see ROAS.
Separate funnel stages. Prospecting, retargeting, and brand as their own lines → honest CPA.
Set a limit. “CPA ≤ €30” or industry-specific level. Make decision limits in advance.
Increase CVR. Better product page/landing, clear CTA, speed → CPA decreases.
Optimize traffic. Negative keywords, audience targeting, creative adjustments.
Scale cautiously. When CPA stays below the limit for 2–3 weeks, increase the budget by 10–20% at once.
Most common mistakes
Mixing with leads. Reported as CPA while measuring a lead → the picture distorts.
Attribution changes. Comparing different models (platform vs. GA4) → the numbers do not match.
Brand in the same basket. Beautifies CPA and conceals the problem in generic.
Slow page. Good targeting can also go to waste if the page is slow.
No quality check. An order is not equally valuable across all segments; track value, not just quantity.
FAQ
What is a “good” CPA?
It depends on the margin and CLV. If the average purchase is €60 and the margin is 50%, a CPA of €20–25 can be effective. Calculate your limits backwards from value.
Why do GA4 and ad platforms show different CPAs?
Attribution and lookback windows differ. Choose primary reporting system (usually GA4) and keep the model the same.
What should I do first if CPA escapes?
Close the most expensive search terms/audiences, replace weak creatives, improve landing conversion rate (headline, CTA, speed).
Can I use CPA in B2B?
Yes, if the “action” is clearly tied to sales (e.g., actual order). For just a lead, use CPL + quality/close rate.
CPA vs. ROAS?
CPA tells the price per conversion; ROAS indicates the return relative to costs. Use both when the value is known.
CTA
Do you want to lower CPA without dropping volume?
Order a campaign audit – we will go through attribution, targeting, and landings, and you will receive a 30-day action list.
