You are correct and the page is wrong. To calculate churn you simply divide the number of churned customers by the number of those customers you had at the beg

You are correct and the page is wrong. To calculate churn you simply divide the number of churned customers by the number of those customers you had at the beginning of the period. Note I mentioned "those" customers, because you need to be looking at the "cohort". You can start the month with 1000 users and end the month with 1000 users and have 100% churn, because you actually lost 1000 users and gained 1000 new ones, so your churn is 100% in this example. The tip about using Stripe customer id's is very helpful. The way we do it is having a cron task running every monday that takes the user_id of all our active users and stores it in the database in a serialized (or jsonb) column. When you want to calculate churn between these 2 dates, you just do [array1] - [array2] and you get the number of customers that churned. Divide that by array1.length and you got your churn %.