What the Cash Runway Calculator Does
Cash runway is the amount of time your business can keep operating before it runs out of money, assuming income and spending stay roughly constant. This calculator turns two simple numbers — your current cash balance and your monthly burn rate — into a clear answer expressed in months and days. It's a core metric for startup founders, small business owners and finance teams anywhere in the world (figures here are shown in dollars, but the maths works in any currency).
The Two Inputs You Enter
- Current Cash Balance ($) – the total cash you have available right now across your accounts.
- Monthly Burn Rate ($) – your net cash outflow each month (total spending minus any incoming revenue). If you're spending more than you earn, this is the gap you fund from the bank.
The Formula
The calculator uses a straightforward division:
- Cash Runway = Current Cash Balance ÷ Monthly Burn Rate
- The whole-number part becomes full months.
- The leftover fraction is multiplied by 30 and rounded to give the extra days.
If your monthly burn rate is zero or negative, runway is reported as 0 — because if you aren't burning cash, you effectively have unlimited runway and the calculation doesn't apply.
Worked Example
Suppose you have a current cash balance of $120,000 and a monthly burn rate of $16,000.
- Runway = 120,000 ÷ 16,000 = 7.5 months
- Full months = 7
- Extra days = 0.5 × 30 = 15 days
So your runway is 7 months and 15 days. The tool also colour-codes the result: under 3 months is critical, under 6 months is a warning, under 12 months is caution, under 24 months is good, and 24+ months is excellent. In this case 7.5 months falls in the "caution" band — a signal to plan fundraising or cost cuts.
Frequently Asked Questions
What's the difference between gross and net burn? Gross burn is total monthly spending; net burn subtracts revenue. This calculator expects your net burn rate, since that reflects how fast cash actually depletes.
How many months of runway should I keep? Many advisors suggest aiming for at least 12–18 months, which is why the calculator flags anything under 12 months as caution and under 6 months as a warning.
Why does it assume 30 days per month? Using a flat 30-day month keeps the day estimate simple and consistent; it's an approximation for the partial month, not an exact calendar count.
