How this calculator works
Burn rate is the average cash a business spends each month. Subtract the closing cash balance from the opening balance to get the cash used, then divide by the number of months. Cash received during the period is already netted out, so this is a net burn figure. Runway divides the closing balance by the monthly burn and estimates how many months remain if nothing changes. A negative burn is a cash build, not a burn, and runway is then not meaningful.
Formula
Cash used = opening balance - closing balance. Monthly burn = cash used / months in the period. Runway = closing balance / monthly burn.
Worked example
Cash falls from $500,000 to $350,000 over six months, so $150,000 was used at $25,000 a month. The remaining $350,000 gives 14 months of runway at the same rate.
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Frequently asked questions
Gross or net burn?
This is net burn because money coming in is included in the closing balance. Gross burn is total cash spent before any revenue, and it is useful for judging operating efficiency rather than survival.
Why is runway missing?
Runway is shown only when cash is falling. If the closing balance is higher than the opening balance, the business is building cash and the runway is unlimited at that rate.
How far ahead should I plan runway?
Many founders aim for 12 to 18 months of runway before raising again, because a raise takes months and a sudden drop in revenue can shorten the runway quickly. Recalculate after any large hire or contract change.