How to use this calculator
- Enter customers at start, customers at end, new customers acquired.
- Choose a display currency, then select Calculate. Results also update after a brief pause while you edit.
- Read the result with the assumptions below. Export details or save a second scenario to compare your choices.
Formula and method
Assumptions and limitations
New customers must be included in the ending count, and retained opening customers cannot exceed the opening cohort.
Worked example
With customers at start = 500, customers at end = 530, new customers acquired = 50, opening-cohort retention is approximately 96%.
What the result means
Retention concerns the original cohort; growth in total customers is a different measure.
Common questions
How should I interpret opening-cohort retention?
Retention concerns the original cohort; growth in total customers is a different measure.
What should I check before using this result?
New customers must be included in the ending count, and retained opening customers cannot exceed the opening cohort.
Methodology and transparency
Calculation specification reviewed on 2026-10-14. Mathematical implementation is tested against independent reference fixtures. This does not imply review by a licensed financial professional. Read the testing and precision policy.