Free tool
Runway and burn rate calculator
Enter your cash balance and what goes in and out each month. This calculator returns your net monthly burn, how many months of runway that buys you, and the month the cash runs out. Runway is cash divided by net burn. It is free, there is no sign-up, and nothing you type leaves your browser.
Runway
6.0 months
Cash runs out around March 2027
- Net monthly burn
- £20,000
- Cash balance
- £120,000
The formula
Runway = cash balance ÷ net monthly burn. Net monthly burn is the cash going out each month minus the cash coming in. Both halves are cash movements, not accounting figures: an invoice you have raised but not collected does not extend your runway, and a cost you have accrued but not paid does not shorten it yet.
A business holding £120,000, collecting £25,000 a month and paying out £45,000 a month has a net burn of £20,000 a month. Divide £120,000 by £20,000 and the answer is six months of runway.
If cash in exceeds cash out, net burn is negative, the balance grows and there is no runway limit to calculate at that rate. That is worth knowing but it is not the end of the question, because a business can be cash-generative in an average month and still run dry in a specific one.
What this number cannot tell you
A runway calculator answers one question well: if this month repeated forever, when would the money run out? No month repeats forever. The figure above is a marker, and these are the things it is silently assuming away.
Burn is flat
It isn't. The month you add two people, sign a lease or start a marketing push, the number that produced your runway stops being the number you are living with.
Every month is an average month
Seasonality moves both halves. A quiet quarter and a strong one average out to a runway figure that describes neither, and it is the quiet one that empties the account.
Money arrives when it is invoiced
Payment terms decide when cash actually lands. A customer moving from thirty days to sixty changes nothing on your P&L and can change everything about the month you get tight.
There are no lumps
Quarterly VAT, an annual insurance renewal, a corporation tax payment, a deposit on equipment. Lumpy outflows are exactly what turns a comfortable average into a bad Tuesday.
Financing does not exist
A loan drawdown, its repayment schedule and its interest all move cash on their own timetable, and none of them appear in a single burn figure.
You get a number, not a path
"Six months" does not tell you which month is tightest, how close you come to zero before recovering, or what happens if you hire the person anyway.
What a forecast does instead
bluprnts is built for the question the calculator has to skip. Instead of one burn figure, you model the things that actually drive the money: your products and prices, the sales you expect and when they land, the people you employ and the ones you plan to hire, your costs, and your financing. From those drivers it derives your bank balance month by month, and reads your runway and your breakeven month off that path rather than off an average.
That changes the answer from a number into a shape. You see which specific month is tightest and how close to zero it gets. You see the effect of a hire in the month it starts rather than smeared across the year. And you can put two versions of the plan side by side, so "can we afford this person?" is a comparison you look at rather than a figure you re-derive by hand.
You do not need accounting data to start. The model is built from what you already know about your business, so a pre-revenue company with nothing to extrapolate can still build a full forecast.
| This calculator | A forecast in bluprnts |
|---|---|
| One burn figure, assumed flat | Burn derived month by month from your actual plan |
| A single number of months | The whole cash path, so you can see the tightest month |
| Re-type the numbers to test a decision | Scenarios saved side by side against your base case |
| Runway only | Runway, breakeven, and a full P&L, balance sheet and cash flow statement |
| A figure you would have to justify | Every figure traceable back to the driver that produced it |
Runway and burn rate questions
- How do you calculate runway?
- Runway is your cash balance divided by your net monthly burn. Net burn is the cash leaving the business each month minus the cash coming in, so a business holding £120,000 and burning a net £20,000 a month has six months of runway. If more cash comes in than goes out, net burn is negative and the business has no runway limit at its current rate.
- What is the difference between gross burn and net burn?
- Gross burn is everything you spend in a month. Net burn is what you spend minus what you collect. Runway is calculated on net burn, because revenue that lands in the bank extends the time your cash lasts. A business with £45,000 of gross burn and £25,000 of monthly receipts has a net burn of £20,000.
- Is a runway calculator accurate?
- It is accurate for the assumption it makes, which is that this month repeats unchanged until the money is gone. That assumption is what makes it quick and what makes it wrong: burn moves when you hire, when a quarterly VAT payment lands, when a seasonal quarter arrives, or when a customer pays sixty days late instead of thirty. Treat the figure as a rough marker, not a date to plan around.
- How much runway should a startup have?
- The common rule of thumb before raising is eighteen months, on the reasoning that a raise takes about six months and you want twelve months of progress to show first. Twelve months is a frequent floor and under six months is usually treated as urgent. These are conventions rather than rules, and they matter less than knowing which month your cash actually gets tight.
- Do I need to sign up to use this calculator?
- No. The calculator runs entirely in your browser, nothing you type is sent anywhere or stored, and there is no email gate. bluprnts is a paid product, but this page is not a trial of it.
See the month it actually gets tight.
Build the forecast the calculator is approximating.
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