ARR (Annual Recurring Revenue) is the single most important metric for any subscription or SaaS business. It tells you the annualised value of all active, recurring contracts — stripping out one-off payments, professional services and anything that is not reliably predictable. This calculator gives you ARR plus the full constellation of metrics investors and operators care about: the MRR bridge, Net Revenue Retention (NRR), Gross Revenue Retention (GRR), your monthly growth rate and an estimate of months to double.
How it works
The calculator starts from your Starting MRR — the monthly recurring revenue at the beginning of the period — and applies five movement types to arrive at Ending MRR:
Ending MRR = Starting MRR + New MRR + Expansion MRR + Reactivation MRR − Churned MRR − Contraction MRR
ARR is then simply:
ARR = Ending MRR × 12
Each movement type has a precise definition. New MRR is revenue from customers who were not paying you at all at the start of the period. Expansion MRR is additional revenue from existing customers — upgrades, seat additions, add-ons. Reactivation MRR is revenue from customers who cancelled previously and then came back. Churned MRR is the revenue lost from customers who cancelled entirely. Contraction MRR is revenue lost from customers who downgraded but did not cancel.
Retention metrics
Net Revenue Retention (NRR) expresses the net effect of all movements on existing customers as a percentage of Starting MRR:
NRR = (Starting MRR + Expansion + Reactivation − Churn − Contraction) / Starting MRR × 100
An NRR above 100 % is the hallmark of a compounding SaaS business: you grow ARR from your existing base even without signing a single new customer.
Gross Revenue Retention (GRR) is the conservative view — it includes only losses (churn and contraction) and is capped at 100 %:
GRR = (Starting MRR − Churn − Contraction) / Starting MRR × 100, max 100 %
Growth rate and doubling time
The monthly growth rate is Net New MRR divided by Starting MRR expressed as a percentage. Months to double uses the Rule of 70 approximation:
Months to double ≈ 70 / monthly growth rate (%)
This is the SaaS equivalent of the Rule of 72 from compound-interest arithmetic.
Worked example
Suppose a B2B SaaS company enters a month with Starting MRR of $50,000 and 200 customers. During the month they sign new contracts worth $8,000, existing customers upgrade generating $3,000 in expansion, two churned customers reactivate adding $500, cancellations cost them $2,000 and a handful of downgrades account for $500 in contraction.
| Movement | Amount |
|---|---|
| Starting MRR | $50,000 |
| + New MRR | +$8,000 |
| + Expansion MRR | +$3,000 |
| + Reactivation MRR | +$500 |
| − Churned MRR | −$2,000 |
| − Contraction MRR | −$500 |
| Ending MRR | $59,000 |
| ARR | $708,000 |
Net New MRR = $8,000 + $3,000 + $500 − $2,000 − $500 = $9,000
NRR = ($50,000 + $3,000 + $500 − $2,000 − $500) / $50,000 × 100 = 102 %
GRR = ($50,000 − $2,000 − $500) / $50,000 × 100 = 95 %
Monthly growth rate = $9,000 / $50,000 × 100 = 18 %
Months to double ≈ 70 / 18 = ~3.9 months
ARR per customer = $708,000 / 200 = $3,540
These numbers reflect a healthy, fast-growing SaaS business: NRR above 100 % confirms existing customers are expanding faster than they are churning, and an 18 % monthly growth rate is exceptional early-stage performance.
Formula note
The ARR = MRR × 12 relationship holds for month-to-month billing. For annual contracts billed upfront, ARR is the sum of the annualised contract value of all active subscriptions — the MRR bridge approach used here is equivalent because it normalises everything to a monthly rate before annualising. Investors may also ask for ARR run-rate, which simply takes the most recent month’s MRR and multiplies by 12 — this calculator does exactly that with your ending MRR.