First-order profitability

Every ecommerce brand runs on one of two acquisition rules, whether it has named it or not. Under first-order profitability, new-customer CAC must be at or below the contribution margin of the first order. Under a payback rule, CAC may exceed first-order contribution as long as measured repeat purchases recover it within a set number of months.

First-order profitability is the conservative rule. It needs no forecast of repeat behavior, it self-funds growth from week one, and it keeps the business safe if retention disappoints. The price is speed: it caps what you can bid, so a competitor willing to wait six months for payback can outbid you for the same customer.

A worked example, as arithmetic. First-order AOV is $90 and contribution margin before ads is 50%, so the first order contributes $45. Under first-order profitability the ceiling on new-customer CAC is $45. If measured cohort data shows a further $60 of contribution within six months, a six-month payback rule would allow a CAC up to $105, more than twice as much, which buys far more volume at the cost of carrying the gap in cash.

The right rule depends on cash, repeat rate, and certainty. A brand with thin working capital, low or unmeasured repeat rates, or a product people buy once should run first-order profitability. A brand with measured cohort retention and cash to carry the gap can run payback. Mixing the two silently, bidding to payback while reporting to first-order, is how businesses discover a cash problem months after they created it.