Funding Runway Calculator
How long your cash lasts when burn is rising or falling each month, and how much you need to raise to reach a target runway.
- Free, no sign-up
- Runs in your browser, nothing is stored
- Formula and worked example included
Funding Runway Calculator
Enter your figures to see results.
How long will my cash last, and how much should I raise?
Runway is the number of months before your cash reaches zero. With £400,000 in the bank and a £35,000 monthly burn growing 3% a month as you hire, you have about ten months, not the eleven a simple division suggests. Enter a target runway to see the funding gap, and a planned raise to see the runway it buys.
How to use this calculator
- Enter cash in the bank and this month's net burn.
- Enter how burn is changing each month: positive if you are hiring faster than revenue grows, negative if revenue is catching up.
- Add a target runway (18 months is typical) and a planned raise to see the gap and the outcome.
What your result means
How to read the figure, what counts as normal, and what to do about it.
Why a straight-line runway misleads
Dividing cash by this month's burn assumes nothing changes. For a growing company that is almost never true: each hire adds to payroll, and the burn in month twelve can be half again what it is today. A team with £400,000 and £35,000 of burn thinks it has eleven months; if burn grows 3% a month it has closer to ten, and the run-out date arrives while the fundraise is still open.
This calculator compounds the monthly change so the runway reflects the trajectory you are actually on. It also runs the sums the other way: how much cash you would need to secure a target runway, and what a specific raise would give you.
How much to raise
Investors generally expect a round to fund 18–24 months: enough to hit the milestones for the next round plus six months to raise it. Work backwards from the milestone plan rather than forwards from what you think you can raise. Then add a buffer (15–20% is common) for the things the plan does not include, and remember that legal fees, and any bridge loan repayment, come out of the gross amount.
The gap figure the calculator shows is before dilution. If you are raising equity, the amount you need and the valuation you can command together determine how much of the company you sell; raising more than you need at a low valuation is an expensive way to buy comfort.
UK funding routes to weigh alongside equity
- SEIS and EIS make angel investment far more attractive to UK investors through income tax relief; make sure you have advance assurance before you pitch.
- Start Up Loans from the British Business Bank offer up to £25,000 per founder at a fixed rate.
- Innovate UK grants for R&D-led businesses are non-dilutive but slow; do not plan runway around a grant that has not been awarded.
- Revenue-based finance suits businesses with predictable recurring revenue and avoids dilution, at a higher cash cost.
- R&D tax credits can be a material cash inflow each year for eligible companies and should be in the forecast.
Worked example: planning a seed round
The company has £400,000 in the bank, burns £35,000 net this month, and expects burn to grow 3% a month as it hires. It wants 18 months of runway and is considering a £500,000 raise.
At constant burn the runway would be 11.4 months. With burn compounding at 3%, the cash runs out in about 10 months.
Eighteen months of the growing burn adds up to roughly £820,000, so the funding gap is about £420,000. A £500,000 raise would take total cash to £900,000 and give roughly 19 months: enough, with a small buffer, to reach the next milestone and raise again.
Frequently asked questions
What is the difference between burn rate and runway?
Burn rate is how fast cash is leaving (pounds per month). Runway is how long the cash lasts at that rate (months). Runway equals cash divided by net burn.
How much runway should a startup have?
At least 12 months at all times, and 18–24 months immediately after a round. Below nine months, fundraising becomes distressed and terms get worse.
Should I include a bridge or overdraft as cash?
Only if it is committed and drawn. An agreed but undrawn facility is a contingency, not runway.
When should I start raising?
When you have 9–12 months of runway left. A seed or Series A round in the UK typically takes three to six months from first meeting to money in the bank, and the process is far easier from strength.
The maths behind this calculator
For anyone who wants to check the working or rebuild it in a spreadsheet.
The calculation
Constant burn: Runway = Cash ÷ Net burn
Changing burn: Each month, Cash = Cash − Burn; then Burn = Burn × (1 + monthly change)
Runway is the month in which cash reaches zero (fractional months interpolated)
Cash for target runway = Sum of the projected burn over the target months
Funding gap = Cash for target − Cash today Assumptions and limits
- Burn changes by the same percentage every month. Real burn moves in steps (a hire, a new office); the smooth curve is a reasonable approximation over a year.
- The raise is assumed to arrive in full today. In practice, rounds close in tranches and legal and advisory fees reduce the net amount.
- Revenue growth is implicitly included in the change to net burn: a negative monthly change means revenue is catching up with costs.
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