Startup Runway (Growing Burn) Calculator
Project how many months of cash you have left when net burn grows every month, not the flat runway a simple cash ÷ burn assumes.
How it works
Month m burn = burn₀ × (1 + growth)^(m−1) · Runway = largest m where Σ burns ≤ cash
A flat cash ÷ burn figure quietly assumes your spend never rises, but a growing team spends more every month. Compounding the burn shortens runway sharply: even a modest 5% monthly increase can cut a naive 10-month runway by a month or two. This calculator walks month by month, subtracting each month’s larger burn until the cash is gone, so you see the real date the tank hits empty.
Worked example
With $500,000 in the bank, a $50,000 net burn this month, and burn growing 5% monthly, month 1 costs $50,000, month 2 $52,500, and so on. The running total crosses $500,000 partway through month 9, giving roughly 8.3 months of runway — noticeably less than the 10 months a flat $50,000 burn would suggest.
Frequently asked questions
Why is my runway shorter than cash ÷ burn?
Cash ÷ burn assumes today’s burn holds forever. If you are hiring and scaling spend, each future month costs more, so the cumulative burn reaches your cash balance sooner than the flat estimate predicts.
What if my burn is shrinking?
Enter a negative growth rate. If burn falls fast enough, the total remaining spend is a finite sum — and if that sum is below your cash balance, the calculator reports that the cash never fully runs out.
Should I use gross or net burn?
Use net burn (cash out minus cash in). Net burn reflects the actual monthly drop in your bank balance, which is what determines how long the cash lasts.
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Educational estimate, not financial advice.