There’s all kinds of churn — dollar churn, customer churn, net dollar churn — and there are varying definitions for how churn is measured. For example, some companies measure it on a revenue basis annually, which blends upsells with churn.
Investors look at it the following way:
Monthly unit churn = lost customers/prior month total
Retention by cohort
Month 1 = 100% of installed base
Latest Month = % of original installed base that are still transacting
It is also important to differentiate between gross churn and net revenue churn —
Gross churn: MRR lost in a given month/MRR at the beginning of the month.
Net churn: (MRR lost minus MRR from upsells) in a given month/MRR at the beginning of the month.
The difference between the two is significant. Gross churn estimates the actual loss to the business, while net revenue churn understates the losses (as it blends upsells with absolute churn).