To calculate your startup runway, divide your cash on hand by your net monthly burn (what you spend minus what you earn each month). The result is the number of months you have before you hit zero. If you have £60,000 in the bank and burn £10,000 a month, that's six months of runway — and the date that turns into is the single most important number to keep in view.
Runway in months = cash on hand ÷ net monthly burn. Cash on hand is the money actually available now. Net monthly burn is your total monthly spend (salaries, tools, rent, everything) minus any monthly revenue. If you make nothing yet, net burn is just total spend.
Turn the answer into a date, not just a count. "Six months" is abstract; "we run out in December" forces decisions. That zero-cash date is what you're really managing — every hire, tool, and experiment moves it closer or further away.
Use real, recent numbers, not the optimistic plan. Average your last two or three months of actual spend, and only count revenue that's genuinely recurring — a one-off payment last month isn't monthly income. Founders routinely overstate runway by ignoring annual bills, taxes, and the costs that hit quarterly.
If your revenue is growing, model burn as a range rather than a single figure: a conservative case where growth stalls and an optimistic one where it continues. Plan against the conservative case. Running out of money is the one mistake you can't iterate your way out of.
There are only two levers: spend less or earn more. Cutting burn is faster and fully in your control — it's why a small, cheap team buys disproportionately more time than a funded one. Raising revenue extends runway and proves the business, but it's slower and less certain.
Watch runway monthly and act early. The dangerous zone is roughly the last three to four months, when you're too low to raise comfortably and too rushed to cut cleanly. Decide "are we raising or cutting?" while you still have six-plus months, not when you have two.
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Free runway calculator — how many months you have left
Runway (in months) = cash on hand ÷ net monthly burn, where net burn is your total monthly spend minus any recurring monthly revenue. £60,000 in the bank at £10,000 net burn a month is six months of runway.
Most founders aim to keep at least six months in view, and ideally 12–18 after a raise. The danger zone is the last three to four months — too low to raise comfortably, too rushed to cut cleanly — so make the raise-or-cut decision well before you get there.
Spend less or earn more. Cutting burn is faster and fully in your control, which is why a small cheap team buys far more time. Raising revenue extends runway and proves the business but is slower — so plan against the conservative case and act early.
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