Why CAC is the wrong north star

Cost per acquisition is easy to measure, easy to report and easy to game. Cut spend on your hardest-to-win segment and CAC improves the same week, while the business quietly gets smaller.

Optimise for contribution, not cost

The number that predicts durable growth is contribution margin per cohort over time. It forces the awkward questions a CAC dashboard lets you avoid: which customers stay, which repeat, and which cost more to serve than they ever return.

Any metric that improves when you stop growing is not a growth metric.

Keep CAC as a guardrail, not a goal. Pair it with payback period and retention by cohort, and let bidding chase the customers who are still with you a year later.