Cash Flow Runway Calculator
Work out how long the cash in your account will last at your current rate of spending.
What is in the bank now, across all business accounts.
Money actually received, not invoiced.
Everything leaving the account: wages, rent, suppliers, tax.
Advanced options
Runway is measured down to this figure rather than to zero.
Cash is not the same as profit
Profit is what you have earned. Cash is what has actually arrived. A business can be profitable on paper and still run out of money because customers pay in 60 days while wages are due every month.
Runway looks only at cash, which is why it is the number to watch when things are tight.
Estimated cash runway
6.4 months
- Current cash
- £40,000.00
- Monthly cash in
- £20,000.00
- Monthly cash out
- £26,250.00
- Net monthly cash burn
- £6,250.00
- Approximate runway in days
- 195
What this means
At the current rate of cash use, your available cash would reach £0 in approximately 6.4 months if income and spending remained unchanged.
Quick answers
- How do I calculate monthly cash burn?
- Subtract average monthly cash coming in from average monthly cash going out. If a business spends £15,000 and receives £12,000 a month, the burn is £3,000 a month.
- Is profit the same as cash flow?
- No. Profit counts income and costs when they are earned or incurred; cash flow counts money only when it actually moves through the bank. A profitable business can still run out of cash if customers pay slowly or a big bill falls due at once.
- What happens if cash inflows exceed outflows?
- There is no runway to measure — the business is building up cash rather than running it down. The calculator shows the monthly surplus instead of a countdown figure.
- How can I extend my cash runway?
- Reduce monthly outflows, increase monthly inflows, or bring in a one-off receipt such as a loan or invoice factoring advance. Cutting costs tends to have a more certain effect than hoping for extra revenue, because a cost saving is confirmed as soon as it is made.
- How often should a small business check its runway?
- Monthly is typical for a stable business, but recalculate immediately after any big change — a large invoice paid late, a new hire, or an unexpected bill — since those events can shorten runway sharply.
Keep your runway under review
Runway moves as customer receipts, supplier payments and one-off costs change, so it is worth recalculating rather than treating a single figure as fixed.
A short runway is information, not a verdict — it usually points at collection timing, cost timing or pricing.
You may also find useful
- Break-Even CalculatorHow many units you need to sell to cover your costs, and to hit a profit target.
- Gross Margin & Markup CalculatorMargin, markup and profit per unit — plus the price you need for a target margin.
- Business Bank Account Cost CalculatorAdd up monthly fees, transfers and cash deposits to see your real banking cost.
How we calculated it
Net monthly cash burn = monthly cash out − monthly cash in. If cash in is the same as or more than cash out, there is no burn and no runway figure — we show the monthly surplus instead.
Spendable cash = current cash + one-off receipt − one-off payment − minimum reserve. Runway in months = spendable cash ÷ net monthly burn. Days are the months multiplied by 30.44, the average length of a month.
The estimated date is today plus that number of days. It assumes cash in and cash out stay exactly the same every month, which real businesses rarely do.
Assumptions
Monthly figures are averages and stay constant, one-off items land inside the runway period, and nothing seasonal or unexpected happens. Runway is measured on cash, not profit — a profitable business can still run out of cash if customers pay slowly.
How this calculator works
Runway is simply how long the money lasts. Take what is in the bank, work out how much more goes out than comes in each month, and divide one by the other. It is the single most useful number to know when things are tight, and it is easy to lose sight of when you are looking at profit rather than cash.
Setting a minimum reserve makes the figure more honest. Most businesses cannot safely run to zero — there is a payroll run, a VAT bill or a supplier payment that has to clear. Measuring runway down to a reserve tells you when you would need to act, rather than when you would fail. If a VAT bill is one of the payments you are planning around, the VAT calculator can help you size it.
The sensitivity option shows how much difference a change would make. Trimming costs by 10% often extends runway more than chasing an equivalent uplift in revenue, because cost savings are certain and revenue is not. Slow-paying customers are a common cause of a short runway even in a profitable business — the late payment interest calculator covers what you can charge when invoices run late.
Worked examples
Six-month runway
A start-up has £18,000 in the bank. It brings in £12,000 a month and spends £15,000, a net burn of £3,000 a month. £18,000 ÷ £3,000 = 6 months of runway, around 183 days — meaning the business would run out of cash in roughly six months if nothing changed.
Positive cash-flow scenario
A consultancy has £15,000 in the bank, takes in £18,000 a month and spends £15,500. Cash in exceeds cash out, so there is a monthly surplus of £2,500 rather than a burn. There is no runway figure to calculate here — the business is adding to its cash balance each month instead of running it down.
Small agency with sensitivity applied
A small agency has £40,000 in the bank. It takes in £20,000 a month and spends £26,250, so it is burning £6,250 a month. £40,000 ÷ £6,250 = 6.4 months of runway, roughly 195 days. Cutting costs by 10% and lifting revenue by 10% takes the burn down to £1,625 a month and stretches the runway to about 24.6 months.
Key terms explained
- Cash runway
- The number of months a business's current cash balance would last at its current rate of net cash burn, assuming income and spending stay the same.
- Monthly cash burn
- The amount by which monthly cash going out exceeds monthly cash coming in. If cash in is higher than cash out, there is a surplus instead of a burn.
- Minimum cash reserve
- An amount of cash a business chooses to keep back rather than spend down to zero, to cover known upcoming costs such as payroll or a VAT bill.
Common mistakes
Using invoiced figures instead of cash received
Runway should be based on money that has actually arrived in the bank, not sales that have been invoiced but not yet paid. Using invoiced figures can make runway look longer than it really is.Assuming a profitable month means cash is safe
A business can show a profit on paper while cash goes down, if customers are slow to pay or a large bill is due. Runway should always be checked on cash, separately from profit.Running the figure to zero instead of a safe reserve
Most businesses need cash in hand for payroll, tax or supplier payments that cannot be delayed. Set a minimum reserve so the runway figure reflects when action is actually needed, not when the account would be empty.Treating the estimate as a guarantee
The runway figure assumes constant monthly cash flows, which real businesses rarely have. Treat it as a planning estimate and update it whenever a large payment or receipt changes the picture.
Common questions
What is cash runway?
It is how many months your available cash would last if money kept coming in and going out at the current rate. It is a cash measure, not a profit measure, which is why a profitable business with slow-paying customers can still have a short runway.
What if I am not burning cash?
Then there is no runway to calculate, and the calculator says so rather than showing a made-up or infinite number. It shows your monthly surplus instead, which is the amount you are adding to the bank each month.
Should I set a minimum reserve?
Usually yes. Running a business to a zero balance is not realistic — there will be a payroll, a tax bill or a supplier payment that has to clear. Setting a reserve tells you when you would need to take action rather than when the money would actually be gone.
How accurate is the estimated date?
It is an estimate based on constant monthly cash flows, which is the one thing you can be sure will not happen. Treat it as a planning marker, and rerun it whenever a big invoice or a big bill changes the picture.
Should I use profit or cash figures?
Cash, always. Use what actually moves through the bank account: money received rather than money invoiced, and bills paid rather than bills incurred. Runway is about the balance, not the accounts.
Why can a profitable business run out of cash?
Because profit is recognised when a sale is made or a cost is incurred, not when cash actually changes hands. A business can be profitable on its accounts while waiting weeks or months for customers to pay, and still run out of money in the meantime.
Last reviewed: 7 September 2026. This calculator is information only and is not tax, accounting or financial advice.