Cheap CAC. Expensive Business.
CAC went down.
Profit did not go up.
Classic trap.
I saw this in channel mixes where cheap traffic entered fast and paid users exited even faster.
The funnel looked cheap at the top. The business was expensive at renewal.
CAC Is One Slice
CAC measures entry cost.
Business health needs a full equation.
margin_after_refunds - servicing_cost - churn_drag
Low CAC with weak retention is still expensive.
Low CAC with high support load is still expensive.
What Happened in My Funnel
Cheaper channels sent users who converted fast and churned faster.
Refund pressure climbed.
Support queue grew.
The headline said “efficient”.
The PnL said “not even close”.
Part of the loss was product-fit churn.
Part of the loss was billing friction.
Decline rate on recurring charges was quite high in this category.
Banks treat this vertical as high-risk merchant traffic.
Ramp-up pricing made it worse in some cohorts.
Scorecard I Use Now
Every channel gets five lines.
- cac
- day_7_active_rate
- refund_rate
- support_tickets_per_100_users
- contribution_margin_per_acquired_user
If only CAC is good, the channel is not good.
What We Changed
We cut spend where margin stayed negative after week one.
We accepted higher CAC on channels with stronger downstream quality.
I also isolate renewal health from pure product retention.
If retention drops with stable engagement and rising declines, I treat it as payments risk first.
Finance got calmer. Growth got less performative.
Trade-Off
You lose easy screenshot wins.
You gain stable economics.
Pick your pain.
Takeaway
Cheap CAC is a cost signal.
Unit economics is the decision signal.
Do not confuse them.
Next: Good Ads. Bad Users..