CAC Payback Period
How many months until a new customer has paid back what you spent to acquire them.
Your numbers
Results
How it works
Payback = CAC ÷ (ARPU × gross margin).
Until a customer crosses payback, they're a loan you made to your own growth. The faster the payback, the faster you can recycle cash into acquiring the next customer — which is why payback, not LTV, is what determines how fast you can grow without raising money.
The classic mistake is dividing CAC by revenue instead of gross profit. A $600 CAC against $50/month of revenue looks like 12 months; against $40/month of actual gross profit it's 15. As a rough anchor, SaaS operators get nervous somewhere north of a year — but the real question is whether your cash can survive the gap.
Worked example
You spend $600 to acquire a customer paying $50/month at 80% gross margin. Monthly gross profit = $40, so payback = $600 ÷ $40 = 15 months. Dividing by raw revenue would have told you 12 months — three months of cash you'd be planning around that don't exist.