Churn Rate Calculator: Customers Lost as a Share of Start
Work out a customer churn rate — the share of customers who cancelled or did not renew during a period — with the retention rate shown alongside.
Adjust the inputs and select Calculate for a full breakdown.
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Churn rate | Retention rate |
|---|---|---|
| 30 of 600 lost | 5.00% | 95.00% |
| 12 of 400 lost | 3.00% | 97.00% |
| 90 of 1,200 lost | 7.50% | 92.50% |
| 5 of 250 lost | 2.00% | 98.00% |
How This Calculator Works
Enter the number of customers lost during the period and the customer base at the start. The calculator divides one by the other and multiplies by 100 to give the churn rate, then shows its complement — the retention rate.
The Formula
Part as a Percentage of a Whole
Part is the portion, Whole is the total it belongs to
Worked Example
Losing 30 customers from a starting base of 600 is a monthly churn rate of 5%, with retention at 95%. A 5% monthly churn implies losing roughly 46% of the cohort over a year, even with no growth in the meantime.
Key Insight
Churn rate is a velocity measure — a small percentage compounds quickly. A 5% monthly churn rate is the same engine as a 46% annual churn, so a number that sounds modest at one cadence can be ruinous at another.
Frequently Asked Questions
How is churn rate calculated?
Divide customers lost during the period by customers at the start of the period, then multiply by 100. Thirty losses from a base of 600 is a 5% churn rate.
What is retention rate?
It is the share of the starting base that stayed — 100% minus the churn rate. The calculator shows it as the complement.
Should I count new customers won during the period?
No. Standard churn uses the starting base only; counting new wins would let growth mask cancellations and obscure the real attrition rate.
Monthly or annual churn — which to use?
Monthly is more responsive and the standard for SaaS reporting; annual is steadier. Be explicit about which cadence a quoted churn rate uses.
How does a small churn rate add up?
It compounds. A 5% monthly churn implies losing roughly 46% of a cohort over a year — the rate is paid each period, on the surviving base.
Related Calculators
Methodology & Review
The churn rate is customers lost divided by customers at the start of the period, multiplied by 100. The complement is the retention rate. The calculation ignores new customers won during the period, which is the standard definition.
Written by Ugo Candido · Last updated May 17, 2026.