Runway Calculator

Growth extends it, if the growth holds.

Growth extends it, if the growth holds. Growth adds runway by shrinking the monthly gap, and that only holds if the growth rate holds.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Currency

Cash available

Monthly revenue

Monthly costs

Monthly revenue growth

Monthly cost growth

Runway

over 10 years

break-even in month 4

Runway at flat revenue8.3 months

Runway with growthover 10 years

Break-even month4

Months growth adds111.8

Growth adds runway by shrinking the gap each month, reaching break-even in month 4. That only holds if the growth rate holds, planning on a rate you have not sustained is how runway calculations mislead.

How the Runway Calculator works

Growth adds runway by shrinking the monthly gap, and that only holds if the growth rate holds. Planning on a rate you have not sustained is precisely how runway calculations mislead the people making them.

Also known as: how long until I run out of money · months of runway left · cash runway calculator

Cash divided by burn, and the assumptions inside it

Runway is available cash divided by net monthly burn, giving the months until the balance reaches zero. It is arithmetic, and every input in it is an assumption.

Available cash means cash you can actually spend. Not the balance including money owed to HMRC next month, not including the processor's rolling reserve, and not including an overdraft that can be withdrawn at the bank's discretion. Deducting known committed payments before dividing gives a number you can plan from.

Burn means forward burn, not backward. Last quarter's average is a starting point and it is not a forecast, particularly if last quarter did not contain a large inventory order and next quarter does.

Why the straight-line number is optimistic

Constant burn is the assumption that makes the calculation simple and the answer wrong. Real burn is lumpy, and the failure point is the first month the balance goes below zero, not the month the average would suggest.

A business with £60,000 and £10,000 average monthly burn has six months of runway on the simple calculation. If month three carries a £25,000 stock order and a VAT payment, it has three.

Which is why the useful version is a monthly cash schedule rather than a division. List opening balance, receipts, payments and closing balance by month for twelve months. The month the closing balance goes negative is the real runway, and it is nearly always sooner than the average implies.

Runway to what

Runway is only meaningful against a milestone. Runway to breakeven is the one that matters for a bootstrapped business: how long until monthly cash generation covers monthly cash consumption.

Runway to a fundraise is the version investors mean, and the convention is that you need enough to reach the next milestone plus the time a raise takes, which is usually longer than founders plan for. Six months of runway when a raise takes four is not comfortable.

For most ecommerce sellers the milestone is more prosaic: runway to the next peak season, when cash comes in. A business with four months of runway in August and a Christmas peak has a different problem from one with four months in January.

Extending it, in order of speed

Fastest is stopping discretionary spend, which for most sellers means advertising. It works immediately and it reduces revenue with a lag, so the runway gain is smaller than the spend cut. Modelling that lag rather than assuming a clean saving is the difference between a plan and a hope.

Next is inventory. Not reordering releases cash immediately and creates stockouts later. Selling existing stock at a discount converts inventory to cash quickly at the cost of margin, and in a genuine cash squeeze that trade is usually correct.

Then the slower structural options: renegotiating supplier terms, chasing receivables, subletting space, moving to a smaller unit. These take weeks or months, which is why they need starting before the situation is urgent, and why the runway calculation is only useful if it is done early enough to act on.

The point at which it becomes a decision

Runway below three months is generally treated as the threshold where the plan changes rather than the spending. Below three months there is not enough time for structural fixes to work, so the options narrow to raising, selling stock at a discount, or cutting hard.

Six months is the point at which most operators should start acting rather than watching, because that is roughly the time a funding conversation or a serious cost restructure takes to complete.

The failure mode is not miscalculating the runway; it is calculating it accurately and waiting. Founders routinely know the number for months before acting on it, because acting means admitting the plan is not working. Setting a trigger in advance, at a specific number of months, converts that into a decision that has already been made.

Where to go next

The Runway question rarely arrives on its own. These are the ones that usually come with it:

Burn Rate Calculator — Gross burn and net burn are different.
Break-Even Timeline Calculator — Two break-evens, months apart.
Ecommerce Startup Cost Calculator — Inventory is the line that grows.
Etsy Fee Calculator — Every Etsy fee on one sale, itemised.

Not financial advice. Marketplace fees change, and they vary by country, plan and seller status. Every rate here is an editable default, not a quoted price, check the platform's current fee schedule before you price a product against it. This is not tax or business advice.

Frequently asked questions

How is runway calculated?

Cash divided by net monthly burn. With growth, it has to be modelled month by month because both revenue and costs move.

How much runway should I keep?

Enough to reach the next milestone plus a margin for it taking longer. Twelve to eighteen months is the common target for a business raising capital; a bootstrapped business usually wants at least six.

Should I model growth in runway?

Model both, flat and growing. The flat case is the floor and the growing case is the plan, and knowing the gap between them is the point of the exercise.

What if break-even is never reached?

Then costs have to change or growth has to accelerate. A model showing no break-even at any horizon is telling you something the spreadsheet cannot fix.