How to calculate MRR by hand
MRR, monthly recurring revenue, is the sum of all active subscriptions normalized to one month:
MRR = sum of (monthly plan price x customers) ARR = MRR x 12
Three rules keep the number honest. Annual and quarterly contracts are divided down to their monthly value, so a 1,200 euro yearly deal is 100 euros of MRR. One-time revenue such as setup fees or consulting never counts. And discounts count at the price actually paid, not the list price.
For the full picture, including the four movements that change MRR every month, read What is MRR? and MRR vs ARR. The one-sentence definitions with growth benchmarks live in the glossary: MRR and ARR.