Your runway is the number of months your cash covers what the business uses up. Enter the cash you have, your monthly spending and your monthly income: you get the runway in months, the date the cash is likely to run out and, if you set a target, how much more cash you would need. Amounts can stay flat or grow by a percentage each month.
Use what goes through the bank
Runway is about cash, not turnover or profit. Count spending when you pay it and sales when the money arrives, VAT included, and add what you pay over to HMRC, such as VAT, PAYE and Corporation Tax, as well as loan repayments. An invoice you have sent but not been paid for is not income yet.
Gross burn and net burn
Gross burn is everything you spend in a month; net burn takes your income off it. It is net burn that drains the bank, so it is net burn that sets your runway. If your figures swing from month to month, use an average of the last few months rather than a single month.
Flat or growing amounts
With flat amounts, the runway is your cash divided by your net burn. If you plan to hire or expect sales to grow, choose ‘Monthly growth’: from month 2, spending and income are multiplied each month by 1 plus the rate you enter. The calculator then shows the month income catches up with spending, if it does.
Buffer, start date and target
The buffer is cash you do not want to touch, such as a month’s payroll: the runway is worked out down to it. The start date is used to date the end of the runway. With a target, such as 12 or 18 months, you see how much more cash you would need and, with flat amounts, the highest net burn that meets it. The month-by-month projection exports as a CSV file for a spreadsheet.
Net burn = monthly spending − monthly income.
Runway (months) = (cash − buffer) ÷ net burn, when net burn is above zero.
With monthly growth, the months are worked out one by one, each amount rounded to the penny, and the month the cash goes below the buffer counts for the share of it the cash still covers. The runway is rounded down to a tenth of a month, so it is never overstated, and the end date assumes spending is spread evenly across the month.
Example: £250,000 in the bank, £32,000 spending and £12,000 income a month
The net burn is £32,000.00 − £12,000.00 = £20,000.00 a month, so the runway is £250,000.00 ÷ £20,000.00 = 12.5 months. Starting on 11 November 2026, the cash runs out around 26 November 2027. To last 18 months you would need 18 × £20,000.00 = £360,000.00, which is £110,000.00 more; with the same cash, the net burn would have to come down to £13,888.88 a month.
