About this calculator
SaaS MRR growth models project Monthly Recurring Revenue over time given starting MRR, new MRR per month (from new logos), churn, and expansion. The output reveals two important truths: how much your business depends on new sales vs retention, and whether net revenue retention is above or below 100%.
The cohort math
Each month: End MRR = Start MRR + New MRR + Expansion − Churn. Compound over 12 months and you see the difference between "Series A" growth (3× ARR/yr) and "lifestyle SaaS" growth (10–20% ARR/yr). The numbers are sensitive — a 1 point churn improvement compounded over 24 months can be 30%+ more MRR.
Net Revenue Retention (NRR) — the most important SaaS metric
NRR = (Starting MRR + Expansion − Churn) / Starting MRR × 100. Above 100% means existing customers grow faster than they churn — your installed base alone produces growth without any new logos. Top-quartile SaaS (Snowflake, Datadog) achieve NRR of 120–140%. Below 100% means you’re running uphill: new sales must offset shrinking existing accounts before any net growth.
Why churn destroys SaaS businesses silently
At 5% monthly churn, you lose 60% of your customer base every 12 months — even before considering revenue churn. The "leaky bucket" problem: pouring water (new MRR) into a bucket with holes (churn) means you need a lot of pouring just to maintain water level. Best-in-class SaaS keeps annual logo churn under 5% and revenue churn (after expansion) often negative.
Expansion: the unsung hero
Seat-based pricing (Slack, Notion), usage-based (Snowflake, Twilio), and tier upgrades (Hubspot) create expansion revenue that offsets logo churn. A typical motion: land a customer at $500/month, expand to $2,500/month over 18 months. Same customer, 5× revenue. Companies that engineer for expansion (vs just acquisition) reach durable growth more easily.
Where this model simplifies
Real SaaS has cohorts that churn at different rates (early customers often churn faster), seasonal sales cycles (Q4 surge, summer slowdown for enterprise), and macroeconomic sensitivity. The simple monthly model gives a useful first-order projection — for board materials, layer in cohort retention curves.