Retention Curve

The retention curve is the single most important chart for product-market fit. Plot cohorts of users (by signup week) and track what % return on Day 1, Week 1, Month 1, etc. A healthy curve flattens — churn slows and a stable base of retained users emerges. A bad curve trends toward zero, meaning you're churning everyone eventually. The shape tells the story: steep drop in first week = onboarding problem, steady decline = weak core value, flat after Month 3 = you've found retention. Retention curves also reveal cohort quality: users from organic search often retain better than paid ads. Top products (Slack, Notion, Figma) flatten around 60-80% retention at Month 6.

Take the cohort of users who signed up in the first week of a month. If 100 signed up, 40 are still active in week 2, 25 in week 4, and it holds near 25 from month 2 onward, the curve has flattened. That flat 25 percent floor is the retained base you can build a business on.