MRR
MRR (Monthly Recurring Revenue) is a measure of recurring revenue on a monthly basis. It includes regular sales encompassing subscriptions and memberships. Variable and one-time fees are not included, among which we can mention implementation fees, additional services, etc.
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Useful links:
https://saasmetrics.co/monthly-recurring-revenue/
https://baremetrics.com/academy/saas-calculate-mrr