Retention

Retention means keeping the users, customers or employees you already have — measured as the percentage who are still active after a set period. In product and design, it's the clearest signal that people find lasting value: if they keep returning, the product works; if they don't, acquisition just fills a leaky bucket. The word literally means the act of retaining or keeping something, and in business it's applied to users, customers, revenue and staff.

You calculate a basic retention rate with a simple formula: retention rate = (users active at the end of a period ÷ users active at the start) × 100, counting only people who were already there at the start — exclude new sign-ups so you measure keeping, not growth. For example, if 1,000 users start the month and 620 are still active at the end, retention is 62%. Its mirror image is churn — the percentage who leave — and for any cohort, retention + churn = 100%.

There are a few common types. User (or customer) retention tracks whether people keep using the product; revenue or net-dollar retention tracks whether the money from existing customers grows or shrinks over time — a strong SaaS figure is above 100%, meaning expansions outweigh cancellations; and cohort retention groups users by when they joined and follows each group's curve over weeks or months. Employee retention is the same idea applied to staff turnover.

The most useful way to see retention is a cohort retention curve — the share of a sign-up cohort still active plotted over time. A curve that keeps falling toward zero means no lasting value; a curve that drops at first and then flattens into a stable plateau is the visual signature of product-market fit, because a core of users has found a reason to stay.

Design drives retention directly. You improve it by nailing onboarding so users reach their first real win quickly (activation), delivering recurring value they can't easily get elsewhere, building habit-forming loops and timely re-engagement, and relentlessly removing the friction and dead-ends that make people quietly drift away. Because it costs far more to acquire a new user than to keep an existing one, small retention gains compound into outsized growth and lifetime value.