The customer churn rate is the share of paying customers at the start of a period who stopped paying during it.
Customer churn rate = customers who churned in the month ÷ paying customers at the start of the month
The denominator matters. Dividing by the customers at the end of the month, or adding the month's new customers, gives a smaller number. Pick one definition and keep it.
A small monthly rate compounds: 3 % a month is about 31 % a year.
sumwerk measures every month against what it started with and marks the running month as measured to date. Churn is also shown per plan, owner or any attribute.
A restricted, read-only key is all it takes. The first import runs in a few minutes; every number you see opens into the customers and Stripe references behind it.