Project 12 Months of Revenue.

The forecaster takes four monthly rates (new-customer growth, expansion, gross churn, contraction) plus a starting MRR and projects 12 months forward. Each month's MRR = previous MRR + new + expansion − churn − contraction. The output is a month-by-month projection table plus your projected ending ARR. It's a simple linear model, not a Monte Carlo simulation; the point is to make the next 12 months legible.

Net new MRR each month = (new) + (expansion from existing accounts) − (gross churn) − (contraction from downgrades). Apply the four rates to the previous month's MRR, sum the deltas, get the new MRR. Compounding 12 months at typical SaaS rates (5-10% MoM net growth) gives 1.8x-3.1x ending ARR; this is why net dollar retention (NDR) matters so much, since it captures expansion minus churn minus contraction in one number per Tomasz Tunguz's analyses.

New growth rate: bottoms-up from your acquisition channels (paid CPLs × conversion rates × pricing). Expansion rate: top-down from your existing-customer revenue growth, typically 1-5% of base MRR per month for healthy B2B SaaS. Gross churn rate: from your cohort retention data (the cohort analysis tool gives you this). Contraction rate: from downgrades and seat reductions; often forgotten and often the largest negative term for usage-based pricing models.

A linear projection assumes the four rates stay constant for 12 months. In practice none of them do: new growth is seasonal, expansion accelerates as customer success engages cohorts, churn rises when a pricing change rolls out, contraction spikes during recessions. Per Bessemer State of the Cloud, the spread between best-case and worst-case 12-month SaaS forecasts is typically ±40%. Use this tool to build a central case, then run it with optimistic and pessimistic variants to define your band.

Monthly during budgeting and quarterly during board prep. Pair with the SaaS metrics calculator for the current-state snapshot, the cohort analysis tool to validate the churn input, and the capacity planner to translate the revenue target into required pipeline and headcount.