The Retention Math Every Founder Should Know: LTV, Churn, and Repeat Rate
You cannot manage what you model wrong. The four numbers that determine whether a loyalty investment pays back — and the traps in each of them.
Loyalty conversations go wrong when they run on vibes — "engagement," "delight," "community." The businesses that get retention right run on four numbers. None of them are complicated; all of them are routinely computed wrong.
1. Repeat purchase rate (RPR)
The share of customers who buy a second time. For most e-commerce, a 20–30% RPR is typical; above 40% is strong. It is the single most honest indicator of product-market fit for retention, because no incentive program can rescue a product nobody wants twice.
2. Churn — measured on a cohort, not a blend
Blended churn hides everything. If you acquired heavily last month, your "average" churn looks great while every cohort is quietly leaking. Always read churn as: of customers acquired in month X, how many were still active in month X+n? Plot three cohorts and you will learn more than from a year of blended dashboards.
3. LTV — with margin, not revenue
The most common LTV inflation: using revenue instead of contribution margin. A $300 revenue LTV at 25% margin is a $75 customer. If acquisition costs $60, you are running a very tight boat while your dashboard celebrates. Loyalty rewards come out of that margin too — a 2% earn rate on a 25%-margin business consumes 8% of your profit pool.
4. Payback window
How long until a cohort's cumulative margin covers its acquisition cost. Under 6 months and you can reinvest aggressively; over 18 and growth is financed on hope. Retention programs move this number more reliably than any acquisition optimization, because every extra order lands inside an already-paid-for relationship.
The uncomfortable conclusion
A loyalty program is a margin reallocation: you tax every transaction to change future behavior. It pays back only if the incremental orders it creates exceed the discounts it hands to customers who would have returned anyway. Estimating that incrementality — not the point balance, not the signup count — is the entire game, and it is why every serious program needs a holdout group from day one.