Runway Calculator

Your startup raised a seed round, you're spending $80K a month on salaries and tooling, and the board wants a runway projection that accounts for revenue growth — not just a flat division of cash by burn. The honest model has to consider current ARR, growth rate, churn, and spend trajectory, none of which stay constant.

Feed in starting cash, monthly burn, current MRR, growth rate, and planned hiring. The calculator projects month by month until cash hits zero or revenue catches up to spend, whichever comes first. Output is a chart, an end-of-runway date, and the moment (if there is one) where you become net cash-flow positive. Treat it as a conversation starter — unknowns like growth holding or customer concentration shifting matter more than the model does.

The model under the hood: each month, starting cash decreases by (gross burn − net new revenue). Net new revenue = (current MRR × (1 + growth rate − churn rate)) − current MRR. Burn is adjusted upward each month if you've planned hires (each hire adds to burn from their start month forward). The projection iterates month by month until cash hits zero or until the end of the planning horizon (typically 18-36 months). Cash-flow break-even happens when monthly revenue exceeds monthly burn — different from runway zero, since you can extend runway by being almost-but-not-quite at break-even and slowing the burn.

A worked example: $1.5M in the bank, $80K monthly burn, $20K MRR, 12% MRR growth, 4% monthly churn (net 8% MRR growth). Net month 1: burn $80K, revenue grows from $20K to $21.6K. Cash drawdown: $80K - $21.6K = $58.4K. End of month 1 cash: $1,441,600. Compound through month 12: revenue is $51K, burn $80K, drawdown $29K, end-of-month cash around $700K. By month 18: revenue $80K, burn $80K, break-even reached. Cash position: roughly $480K, plus any profitability after break-even. Runway in this scenario is fine — break-even before cash runs out. Now sensitivity-test: if growth drops from 12% to 6%, revenue at month 18 is only $48K against $80K burn, and runway runs out around month 22. The model shows where the assumptions actually matter.

Where this stops being a serious financial plan: customer concentration, lumpy enterprise contracts, seasonal patterns, and the difference between MRR and recognized revenue all matter for real corporate finance. The simple model assumes smooth growth and constant churn; reality has cohort effects, win/lose lumpiness, and macro factors. Treat the calculator as a back-of-envelope sanity check. For board presentations, build a proper financial model in a spreadsheet with scenario tabs (best case, expected, downside) and clearly labeled assumptions. Most failed startup post-mortems trace back to over-optimistic assumptions in this exact category — model conservatively, fundraise early when runway falls below 9 months, and don't trust a single-line projection that doesn't show its sensitivity to growth and churn assumptions.