Cost per lead is the only number that tells you whether the channel works. Reach, impressions and follower counts are all proxies for it.
The formula
Total spend for a period divided by leads in the same period. The division is easy; the honesty is in what goes into the numerator.
- The subscription. Usually the most visible and the smallest part.
- Accounts. Purchase plus replacement of the ones that get limited. Count it monthly, not as a one-off.
- Proxies. One per account. Sharing them is how you lose a whole batch at once.
- Model calls. Every comment and every reply is a paid request on your own key.
- Your time. An hour of setup costs what an hour of your work costs.
Why month one lies
New accounts warm up: the daily limit grows over roughly a month while the spending is already full. Cost per lead in that month is inflated by design. That is an investment, not a loss — but it is also not your steady-state number.
The opposite mistake is more common. Month two looks great, so the account attrition never makes it into the model. Six months later the fleet needs replacing and the earlier profit turns out to have been borrowed.
What to compare it against
Two things: the cost of a lead from your other channels, and what a lead is worth to you. A cheaper lead that closes at half the rate is not cheaper. The comparison that matters happens in revenue, not in lead counts.
The account side of the number is broken down in the piece on what an account fleet costs, and the daily ramp is in the warm-up calculator.