Retention Rate Calculator
Calculate customer retention and project how a cohort decays over time.
What the Retention Rate Calculator does
Retention rate measures the share of existing customers who stay. New acquisitions are excluded, because including them would mask churn behind growth — the classic leaky bucket problem.
Formula
Retained = Ending customers − New customersRetention % = Retained ÷ Starting customers × 100Share remaining after n periods = Retention^n
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Customers at the start | number | Yes | Accepts 1 or more. |
| Customers at the end | number | Yes | Accepts 0 or more. |
| New customers acquired | number | Optional | Accepts 0 or more. |
| Project forward | periods | Optional | Accepts 0 or more, up to 120. |
How to use it
- Enter Customers at the start and Customers at the end.
- Optionally add New customers acquired and Project forward.
- Select Calculate.
Worked example
Starting with 800 customers, ending with 870 after acquiring 130.
- Start
- 800
- End
- 870
- New
- 130
Retained 740 of 800 — a 92.5% retention rate and 7.5% churn.
Frequently asked questions
Why exclude new customers from retention?
Because retention measures whether you keep the customers you already had. Including new ones lets rapid growth disguise a serious churn problem.