What is CPA?
Cost per acquisition, the advertising spend required to produce one conversion.
CPA = Ad Spend / Conversions
A worked example
You spend Rs 90,000 in a month and record 60 purchases, giving a CPA of Rs 1,500. If your contribution margin per order is Rs 1,200, that campaign is losing Rs 300 on every sale while the dashboard shows 60 conversions and looks busy.
Why it matters
CPA is the number that decides whether a campaign should exist. Every other paid metric feeds into it, and none of them replaces it: a good click-through rate with a bad CPA is an expensive way to be liked.
Your ceiling is set by contribution margin, not by what feels affordable. Work out what remains after cost of goods, shipping, packaging, payment charges and expected returns, and that figure is the most you can pay for a customer before the sale costs you money. Some businesses deliberately exceed it during a launch to buy volume and reviews, which is a legitimate choice as long as it is a choice rather than an oversight.
CPA also differs from CAC in a way that matters when you report to anyone. CPA counts media spend against conversions. CAC counts everything, including agency fees, tooling and creative, against genuinely new customers. Quoting CPA when someone asked for CAC understates your real cost by thirty to fifty per cent.
The nuance most people miss
A blended CPA across new and returning customers is close to useless, because returning customers convert far more cheaply and drag the average down. A campaign that looks like it produces Rs 900 acquisitions may be producing Rs 400 repeat purchases and Rs 2,400 new customers, and only the second number tells you whether you can grow. Separate prospecting from remarketing before you set any target.
Common mistakes
- Setting a CPA target from a competitor or a blog post rather than from your own contribution margin
- Blending prospecting and remarketing, which hides the real cost of acquiring anyone new
- Quoting CPA when the question was about CAC, which excludes fees, tooling and creative cost
- Judging CPA before the account has enough conversion volume for the figure to mean anything