Customer Churn Rate CalculatorFree online financial calculator — instant results, no sign-up
Calculate period churn and retention from starting customers and customers lost.
Estimates only, based on the inputs and assumptions shown. This is not financial, investment, tax, or legal advice. Prices, rates and local rules may change; crypto scenarios do not predict returns. Confirm important decisions with a qualified professional.
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About the Customer Churn Rate Calculator
The Customer Churn Rate Calculator measures the percentage of customers present at the start of a period who were lost during that period, along with the percentage retained. With 1000 starting customers and 45 starting customers lost, it returns a customer churn rate of 4.5% and a customer retention rate of 95.5%. New customers acquired during the period are excluded from these calculations.
- Customers at period start
- The number of customers in the opening customer base for the period being measured, entered in customers.
- Starting customers lost
- The number of customers from that opening customer base who were lost during the same period, entered in customers.
Formula and method
C = (L / S) × 100; R = ((S − L) / S) × 100 = 100 − C.
- SNumber of customers at the start of the period; must be greater than zero.
- LNumber of starting customers lost during the period; must be between zero and S.
- CCustomer churn rate, expressed as a percentage.
- RCustomer retention rate, expressed as a percentage.
Divide starting customers lost by customers at period start, then multiply by 100 to obtain the churn percentage. Subtract that percentage from 100 to obtain retention. For the default inputs, (45 / 1000) × 100 = 4.5% churn, and 100 − 4.5 = 95.5% retention.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Customers at period start1000 customers
- Starting customers lost45 customers
Results
- Customer churn rate4.5%
- Customer retention rate95.5%
How to use the Customer Churn Rate Calculator
- 1Choose a measurement period and a consistent definition of when a customer counts as lost.
- 2Enter Customers at period start; the default is 1000 customers.
- 3Enter Starting customers lost; the default is 45 customers, counting only losses from the opening customer base.
- 4Check that both inputs are whole-number counts, the starting count is positive, and losses do not exceed the starting count.
- 5Read the customer churn and retention outputs; the default inputs produce 4.5% and 95.5%, respectively.
Reading your result
Customer churn rate shows the share of the opening customer base lost during the selected period: 4.5% means 45 of the 1000 starting customers were lost. Customer retention rate shows the complementary share retained: 95.5% means 955 of those starting customers remained. The two rates sum to 100%; neither output measures growth from newly acquired customers.
Limitations
This calculator measures customer-count churn, not revenue churn, profitability, or total customer-base growth. It assumes losses refer only to the starting customer base and that each customer is counted once under a consistent loss definition. Reactivations and temporary pauses require a defined counting policy because the tool does not track customer activity. A zero starting count makes the rates undefined. Results describe only the selected period and should not be compared across different period lengths without adjustment.
Common questions
Should I include customers acquired and lost during the period?+
No. Neither input should include customers acquired after the period began, even if they also leave before it ends. This calculator tracks losses only among customers present at the start.
Why is retention 95.5% when churn is 4.5%?+
Both rates use the same opening customer base. Of 1000 starting customers, 45 were lost and 955 were retained, so retention is (955 / 1000) × 100 = 95.5%, which also equals 100% minus 4.5%.
Can I enter more lost customers than starting customers?+
No. Losses from the opening customer base cannot exceed that base. If your loss count is larger, check for duplicate records or customers who joined after the period began.
Is the default 4.5% churn rate monthly or annual?+
It is the rate for whichever period your inputs cover. It is monthly only if the 1000 starting customers and 45 losses describe the same month, and annual only if they describe the same year.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.