How long it takes to recover the cost of acquiring a customer from the contribution margin they generate. Payback is the bridge between unit economics and cash flow: a brand can be profitable on paper and still run out of money if payback is too slow. The faster you recover CAC, the faster you can recycle that dollar into the next customer.
Benchmark. Under 3 months is excellent, 3-6 is the healthy standard for DTC, 6-12 is workable, and over 12 is fragile. In the 6-12 zone you are effectively financing your customers' purchases, which only works with cheap capital.