Cohort Retention Calculator
How many of a starting cohort remain after each month at a steady retention rate — the survivors at one, three, six and twelve months, the cohort's half-life, the average customer lifetime and the revenue the cohort earns over it.
If a cohort keeps a fixed share of its customers each month, the survivors fall geometrically: 90% retention leaves 53% after six months and 28% after a year.
How the cohort retention calculator works
If a cohort keeps a fixed share of its customers each month, the survivors fall geometrically: 90% retention leaves 53% after six months and 28% after a year. The expected lifetime of a customer is one over the churn — ten months at 90% — and multiplying by monthly revenue per user gives what the cohort is worth. The half-life says when half have gone; it is the number that makes retention rates comparable.
Formula: survivors(n) = N × r^n; lifetime = 1 / (1 − r); half-life = ln 0.5 / ln r; cohort value = N × ARPU × lifetime
Worked examples
| Inputs | Customers left after 12 months | Note |
|---|---|---|
| 90% monthly retention | 282.4 | 28% left after a year |
| Best in class | 693.8 | a 33-month lifetime |
| Leaky | 31.7 | gone in a few months |
FAQFrequently asked questions
What is cohort retention?
Following the customers who joined in one period and measuring how many remain each period after. It separates the health of the product from the noize of new sign-ups.
Why does a steady rate decay so fast?
Because it compounds: 90% of 90% of 90%. Twelve months of 90% retention keeps 28% of the cohort, not 90%.
What is a good monthly retention rate?
Above 95% for business software, 85 to 92% for consumer subscriptions, and lower for apps that are used seasonally. The half-life row is the easiest way to compare.
Does retention really stay constant?
Usually it improves with tenure — early leavers go quickly, survivors stay longer. A constant rate is a conservative first estimate; a curve fitted to real cohorts is better.
How does this give lifetime value?
Average lifetime is one over the monthly churn; times monthly revenue per customer, that is the revenue a customer brings over their life — the marketing side of the LTV calculation.
Where these figures come from
- Interactive Advertising Bureau — measurement guidelines — the impression and viewability definitions CPM depends on
- US Federal Trade Commission — the US advertizing regulator
Last checked: September 2026. These are standard industry definitions; where platforms disagree, the page says so.