Calculation desk / growth
Churn Rate Calculator
Calculate customer churn and retained customers for a reporting period.
Churn Rate Calculator: Measure the share of a starting customer group that left during one reporting period. The result pairs customer churn with the number retained from that starting group, so new sign-ups cannot hide losses among existing customers. Runs 100% locally in your browser with zero server file uploads.
- Category
- Calculators
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Customer churn rate
4.5%
- Customers retained
- 955
Churn rate = customers lost ÷ starting customers × 100- Starting and lost customer counts use the same cohort and time period.
- New customers added during the period are excluded from this simple churn formula.
Formula and worked example
Churn rate = customers lost ÷ starting customers × 100
A worked example with sample values:
| Inputs | |
|---|---|
| Customers lost | 45 |
| Starting customers | 1,000 |
| Results | |
|---|---|
| Customer churn rate | 4.5% |
| Customers retained | 955 |
Starting cohort: formula and example
Customer churn (%) = customers lost ÷ starting customers × 100. Customers retained = starting customers − customers lost. Losing 45 out of 1,000 gives 45 ÷ 1,000 × 100 = 4.5% churn and 1,000 − 45 = 955 retained. Label this monthly or annual according to the dates behind the counts.
No departures gives 0% churn; losing the entire starting cohort gives 100%. Losses cannot exceed the starting count. The retained output is not the business's closing customer total because this calculation excludes acquisitions, reactivations and any other movement outside the original group.
Compounding monthly losses
Keeping 95.5% of survivors each month leaves 0.955^12 of the original group after a year. Annualised churn is therefore (1 − 0.955^12) × 100 ≈ 42.45%, rather than 4.5 × 12 = 54%. These are hypothetical figures, and constant churn is a modelling assumption rather than a forecast.
OpenStax explains exponential change as repeated multiplication over equal intervals (https://openstax.org/books/precalculus-2e/pages/4-1-exponential-functions). For varying monthly rates, multiply the twelve retention factors, then subtract that product from one. Converting an annual fraction a back to an equivalent constant monthly fraction uses 1 − (1 − a)^(1/12); actual monthly observations can still differ.
How to use it
- Enter values that cover the same scope and reporting period.
- Choose a display currency when the calculation includes money.
- Calculate, then review the formula and assumptions beside the result.
Privacy & limitations
Every value and calculation stays in your browser. This is a planning utility, not accounting, tax, legal, or investment advice. Verify material decisions in your source system and with an appropriate professional.
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Frequently asked questions
Do new customers belong in the starting count?
Only customers present at the beginning belong in this denominator. Count departures from that same group. Someone who joins and leaves within the period is outside this simple starting-cohort measure; including that departure alone would mix populations.
Can I turn monthly churn into annual churn by multiplying by twelve?
Not for a constant percentage lost from the remaining cohort. Each month has fewer survivors to lose. With monthly churn m written as a decimal, annual churn is 1 − (1 − m)^12 under a constant-rate assumption. The tool itself calculates only the period you enter.
Is customer churn the same as revenue churn?
No. Losing one small account and one large account counts equally here, even if their revenue differs. Revenue churn needs lost revenue and a starting revenue base, with an explicit treatment of upgrades and downgrades. Those amounts are not inputs on this page.
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