Burn Rate & Runway Calculator
Calculate your net monthly cash burn and exact financial survival runway in real time.
1. Enter Company Metrics
2. Live Calculations
Remaining Survival Runway
How to Use This Calculator
What the numbers mean
Your net burn rate is simply how much cash actually leaves your business each month once you account for what's coming in. It's not the same as your total spending, and that distinction catches a lot of founders out.
The maths is straightforward: Net Burn = Monthly Expenses - Monthly Revenue So if you spend £25,000 a month and bring in £12,000, you're burning £13,000. That's the figure that matters, because it's what your bank balance drops by.
Once your revenue covers your costs, net burn goes to zero or below. At that point you're no longer dependent on the money in the bank lasting — you can keep going indefinitely.
Reading your runway
Divide your cash by your net burn and you get your runway — the number of months before you run out. £130,000 in the bank burning £13,000 a month gives you ten months.
Most UK investors and finance directors suggest keeping 12 to 18 months of runway. That's not an arbitrary number: raising a funding round realistically takes three to six months, so anything under a year means you're starting the next raise almost immediately, usually from a weak position.
It's worth running a few versions. Try it with a bad month of revenue, or with a hire you're considering added to expenses. Seeing how much a single decision moves your runway is usually more useful than the headline number itself.
A worked example
Numbers are easier to trust when you can follow them all the way through. Take a small UK software company with £150,000 in the bank, £18,000 a month going out, and £6,000 of monthly recurring revenue coming in.
| Step | Working | Result |
|---|---|---|
| Net burn | £18,000 − £6,000 | £12,000/mo |
| Runway | £150,000 ÷ £12,000 | 12.5 months |
| After a £40k hire | £150,000 ÷ £15,418 | 9.7 months |
That third row is the one worth sitting with. A £40,000 salary costs roughly £41,000 a year once Employment Allowance covers the National Insurance, which is about £3,418 a month. Adding one person takes nearly three months off the runway — and the decision looks very different at 9.7 months than it does at 12.5. We go through where that £41,000 figure comes from in what your first hire really costs.
Four ways this calculation goes wrong
The arithmetic is trivial. Getting the inputs right is where it actually goes wrong, and these four account for most of it.
- Using invoiced revenue instead of collected cash. Revenue you have earned but not been paid is useless for making payroll. If your customers pay at 60 days, your real cash position trails your revenue figure by two months. Use what is actually in the bank. Our guide on getting paid on time covers what you can do about it.
- Forgetting the bills that don't arrive monthly. Corporation Tax, VAT quarters, annual insurance and accountancy fees don't show up in a typical month, so they get left out and then land all at once. Divide the annual total by twelve and include it. The cost of running a company guide lists what to expect.
- Assuming revenue holds steady. A runway figure calculated on current MRR quietly assumes no customer ever leaves. If you're losing 3% of revenue a month, your real runway is shorter than the calculator suggests — see churn and your runway.
- Treating one number as the answer. A single runway figure is a snapshot of assumptions that will all turn out slightly wrong. Run an optimistic case and a pessimistic one. The gap between them tells you more than either number alone.
Where to go from here
If your runway is under 12 months
You have two levers: spend less or earn more. Start with stretching your runway for cuts that don't involve losing people, then look at funding and tax relief — R&D credits and the venture capital schemes can add months without giving away equity.
If you're thinking about raising
Start earlier than feels necessary. A round takes three to six months, so raising at nine months of runway is comfortable and raising at four is not. Before a seed round covers the numbers and paperwork investors ask for.
If you want to stop burning entirely
Work out the revenue that would take you to zero net burn with the break-even calculator, which also tells you whether you're default alive or default dead at your current growth rate.
If you're just starting out
How burn rate works explains the terminology properly, and sole trader vs limited company covers a decision worth getting right early — the answer changed in April 2026.
Questions people ask
Is gross burn or net burn the right number?
Net burn, for runway. Gross burn is your total monthly outgoings ignoring revenue, which matters when you want to know how big your cost base is, but it overstates how fast your bank balance is falling if you have any revenue at all.
Should I include my own salary?
Yes, if you're taking one. A runway figure that excludes founder pay describes a company that doesn't exist. If you're currently unpaid but plan to start paying yourself, run it both ways so you can see what that decision costs in months.
What counts as a healthy runway?
Commonly cited guidance is 12 to 18 months. The reasoning is that raising takes three to six months, so a year gives you room to start the next raise from a position of choice rather than necessity. Below six months, most decisions stop being strategic.
Does this send my figures anywhere?
No. The calculation runs entirely in your browser using JavaScript. Nothing you type is transmitted, logged or stored — there's no server to send it to. See the privacy policy for the full detail.
What does "cash flow positive" mean here?
If your revenue is equal to or greater than your expenses, net burn is zero or negative and there is no runway to calculate — you aren't losing money, so the cash in your account isn't a countdown. The calculator shows that instead of a month figure. Note that it's a statement about this month, not a guarantee about next month.