What a cashflow runway actually is, and how to read yours

Most small businesses that fail were not unprofitable on paper. They ran out of cash while waiting for that profit to turn up. A company can be growing, winning awards and invoicing record numbers, and still miss payroll because the money is tied up in unpaid invoices and stock. Runway is the number that warns you long before that happens.

What runway really means

Runway is how many months your business can keep operating at its current rate of spending before the bank balance hits zero. It answers the only question that matters in a crisis: if nothing changes, how long have I got?

The formula is deliberately simple. Take the cash you actually hold, and divide it by your average monthly net burn — the amount more you spend than you bring in. If you hold 30,000 pounds and you burn 5,000 pounds a month, you have six months of runway.

It is the most honest number in the business. Revenue can be flattered by a single large invoice. Profit depends on judgement calls about what counts as a cost and when. Runway is just cash divided by burn, and it does not care about any of that.

A worked example

Imagine a small agency with 48,000 pounds in the bank. Over the last three months it brought in an average of 22,000 pounds and spent an average of 26,000 pounds. That is a net burn of 4,000 pounds a month.

48,000 divided by 4,000 is twelve. Twelve months of runway. Comfortable, but not infinite — and crucially, the owner now knows that a single quiet quarter would not sink them, while two consecutive lost clients would start a countdown.

Gross burn versus net burn

There are two ways to measure burn, and confusing them is the most common mistake. Gross burn is everything going out. Net burn is what goes out minus what comes in. For runway, you almost always want net burn, because your revenue keeps refilling the tank while you spend.

The exception is a stress test. If you want to know your worst case — what happens if revenue stops entirely — use gross burn. That is your true survival floor, and it is worth knowing.

Why a three-month average

A single month can lie in both directions. A big client paying early, or a quarterly VAT bill leaving, can swing one month wildly. Averaging the last three months smooths out that noise and gives you a figure you can plan around. If your business is highly seasonal, look at the same period last year as well.

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Check your runway on the first working day of every month. It takes five minutes and it is the single most useful habit a small business owner can build.

What different runway lengths mean

• Twelve months or more: you have room to invest, hire, or absorb a bad quarter. Spend it deliberately, not nervously.
• Six to twelve months: healthy, but watch the trend. A runway shrinking by a month each month is more worrying than a short runway that is stable.
• Three to six months: time to act. Not panic, but a clear plan to raise the number, starting this week.
• Under three months: this is the priority above almost everything else. Protect cash aggressively and move fast.

How to extend your runway

Runway has two ends, and you can pull on both. To bring cash in sooner: invoice the day work is done, shorten payment terms, take deposits, and chase overdue invoices without apology. To slow cash going out: review every subscription, renegotiate or stage large costs, and delay non-essential spend until the picture is clearer.

The trap is treating runway as a fixed fact rather than a lever. A business with three months of runway and a plan is in a far stronger position than one with six months and no idea which direction the number is heading.

Fincharta calculates your runway automatically from a single bank statement, tracks the trend month to month, and tells you in plain English which way it is moving. See a sample report.