Journal · January 2026
A payback window is not lifetime value
One is a cash question with a date. The other is a contribution question with an honest horizon. UA teams that fuse them buy the wrong weeks.
Payback asks: after store fees, VAT, refunds, and variable support, when does this cohort return the baht we spent to acquire it? Lifetime value asks: given a horizon we can defend, what contribution remains after those same costs — including the ones that arrive late, like incentives and creative refresh?
A cohort can pay back on day 38 and still be a poor lifetime bet if month-three incentives and chat-support load erase the tail. Another cohort can miss a 30-day payback target and still be the right buy because annual plans throw off quiet margin after day 90. Collapsing both into “D30 ROAS” is how networks that front-load revenue win the weekly meeting.
Write two rules, not one tile
In Payback & CAC Discipline we ask teams to publish a kill-rule (if payback exceeds N days on this rail, pause) and a separate hold-rule (if predicted net LTV at horizon H is below CAC × k, do not scale). The numbers differ by product. The important part is that they are not the same sentence.
k is not sacred. Some Bangkok consumer apps use 1.3 because creative dies fast; some B2B-ish utilities use 1.1 because support is cheap. Pick it in a room with finance, then stop moving it every time UA wants more budget.
What “never” should mean
If a cohort has not paid back by your fuse date and the remaining curve is flat after incentives, say “never” on the ledger. Do not invent a 720-day tail to rescue the campaign. Vault Nodehub worksheets use “never” as a first-class status. It keeps people honest.