Churn and Retention Calculator
Enter the customers you had at the start, those you lost and those you gained. You get churn, retention, average lifetime, value per customer and a 12 month outlook.
Worked examples
Four percent a month
500 customers, 20 lost, 35 gained, 1 month, £30 a month at 80% margin
38.7% lost over a year
Lifetime is 25 months, so lifetime value is £30 x 80% x 25 = £600. The count ends the month at 515.
A quarter
1,000 customers, 100 lost in 3 months
10% for the quarter, 3.5% a month
The matching monthly rate is 1 - 0.9^(1/3) = 3.45%, so the average customer stays about 29 months.
Where it levels off
4% monthly churn, 35 new customers a month
About 875 customers
35 divided by 0.04 is 875. The count rises towards that figure but never passes it.
About Churn and Retention Calculator
Churn is the share of customers you lose over a period. It sounds simple, but a few details change the answer. Only customers you had at the start can be lost, so new customers are left out of the calculation. And a rate for a quarter is not three times the monthly rate, because each month you start with fewer customers. This calculator takes the customers you began with, the ones you lost and the ones you gained, and works out the churn for the period, the matching monthly and yearly rates, and the retention rate.
Churn also tells you how long a customer stays. If you lose 4% a month, the average customer stays about 25 months. Combine that with the revenue each customer brings and your gross margin and you have a lifetime value to set against the cost of winning a customer. A table then carries on at the same churn and the same pace of new customers for the next 12 months, so you can see whether the customer count keeps growing or levels off at a ceiling.
How to use Churn and Retention Calculator
- Enter the customers you had at the start of the period, the number you lost and the number you gained.
- Enter the length of the period in months, so a quarter is 3.
- Add the revenue per customer each month and your gross margin to see a lifetime value.
- Read the churn, the lifetime, the cohort table and the 12 month outlook.
Common uses
- Tracking subscribers, members or clients
- Judging how much you can spend to win a customer
- Seeing where the customer count will settle
- Comparing this quarter with last quarter on the same basis
Sources
Last reviewed 18 October 2026.
Frequently asked questions
How is churn calculated?
Customers lost divided by customers at the start. A business that began with 500 customers and lost 20 has 4% churn. Customers who joined and left within the period are left out of the starting count.
How is the yearly churn worked out?
From the monthly rate with compounding: one minus the monthly retention raised to the power of twelve. At 4% a month, about 38.7% of customers are gone after a year, not 48%.
What does the average lifetime mean?
It is one divided by the monthly churn rate. With 4% monthly churn, a customer stays 25 months on average. It is an average, so some leave much sooner.
What is lifetime value here?
Revenue per customer each month, times gross margin, times the average lifetime in months. It is a rough guide that assumes churn and revenue stay the same.
Why does the customer count level off?
Because the number you lose rises as the base grows, while you add a steady number. The count settles where the two are equal: new customers each month divided by the monthly churn rate.