Estimate months of runway remaining with current cash, monthly burn rate, revenue growth, and funding round planning scenarios.
A startup runway calculator converts a cash balance, a monthly burn rate, and optional revenue and funding inputs into the answer founders ask first: how many months until the company's cash hits zero. The calculation runs month by month, so revenue that grows each month shrinks the effective burn and extends the runway beyond what simple division suggests, and a planned funding round can be slotted in at a chosen month. The thing people most often get wrong is the burn figure: entering gross burn (expenses alone) instead of net burn (expenses minus revenue) can shorten the reported runway by months.
A concrete input and expected output from the current implementation.
Input
Cash on hand: $300,000 | Monthly expenses: $50,000 | Monthly revenue: $10,000, growing 10% per month | No funding round
Expected output
Runway: about 8.5 months. Cash runs out during month 9 (8 full months plus part of month 9). By comparison, a flat calculation using the current $40,000 net burn ($50,000 expenses minus $10,000 revenue) would say 7.5 months.
Because revenue grows 10% each month, net burn shrinks month by month: $40,000, then $39,000, then $37,900, and so on down to $28,564 in month 9. Cumulative burn across 8 months is $285,641, leaving $14,359, which month 9's burn exhausts about halfway through, hence roughly 8.5 months.
The core relationship is runway = cash on hand divided by net monthly burn, where net burn is cash going out (salaries, rent, vendors) minus cash coming in from revenue. With no growth and no funding entered, the result is a straight division: $300,000 in cash at a $40,000 net burn gives 7.5 months. This matches the formula in most spreadsheet runway models.
When revenue growth or a funding round is entered, the calculator simulates each month in sequence: revenue grows by the stated percentage, which lowers that month's net burn, and a round adds its proceeds in the month you specify. Runway is the month cumulative outflows cross the starting cash balance. Because growth compounds, a small change in the growth rate moves the result by months, not weeks.
Enter net burn, meaning monthly expenses minus revenue, because that is the number that actually drains your bank balance. Entering gross burn (expenses alone) ignores the revenue already offsetting costs and understates runway. If you have revenue, keep it in one place: either deduct it from the burn figure you enter or put it in the revenue field, not both.
Only if every input holds. The output is arithmetic performed on estimates: your burn figure is a forecast, revenue growth compounds, and the calculator cannot see cash-flow timing, such as a big invoice paid late or payroll landing on a different day. Use the result to compare scenarios and set a decision date, not as a prediction of the exact month you run out.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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