Financial Runway

Financial runway is the length of time a business can continue to operate before it exhausts its available cash, calculated by dividing the cash it holds by the rate at which it is consuming cash. A business with $240,000 in the bank consuming $30,000 a month net of collections has eight months of runway. The figure is conventionally quoted in months, and the term is used most heavily by early-stage and unprofitable businesses, for which the cash balance rather than the profit figure determines how long they have.

The denominator is the burn rate, which the Securities and Exchange Commission defines as "the rate at which a company spends its cash over time, frequently discussed as a monthly rate." Because that measure has no standard computation and comes in a gross form and a net form, a runway figure is only meaningful alongside a statement of which burn it was divided by. Runway computed on gross burn ignores every dollar the business collects and is therefore far shorter than the business's real position; runway on net burn is the one people normally mean.

The division is trivial and the inputs are not. Runway is one of the few business figures where the formula is genuinely simple and the number is still routinely wrong, and there are three reasons for that.

The first is the numerator. "Available cash" is not the same as the bank balance. Money already committed to a payroll run three days away is not available. A tax deposit accrued but not yet paid is not available either, even though it is sitting in the account. In the other direction, an undrawn committed line of credit is available in a real sense, and a business that ignores it understates its position, while a business that counts an uncommitted facility a lender can withdraw overstates it. The honest practice is to compute runway on cash alone and state any standby credit separately.

The second is the denominator, and it is where nearly all the error lives. A single month's burn is a data point. Dividing by it and calling the answer "runway" assumes the business will spend at exactly that rate for however many months the arithmetic returns, and almost no business does. A month containing an annual insurance premium produces an artificially short runway; a month in which a large receivable happened to land produces an artificially long one.

The third is that the whole figure is a statement about the future computed entirely from the past.

Runway on current burn and runway on projected burn are different numbers, and they answer different questions. The snapshot version divides today's cash by a trailing burn figure. It is the right number for the question "if nothing changes, when do I run out?", and it is the wrong number for a business that is about to make a decision. A business planning to hire two people next month has a shorter runway than its snapshot says. A business whose revenue is climbing has a longer one, because net burn falls as collections rise, and the effect compounds: each month of growth lengthens the remaining runway rather than just consuming one month of it.

This is why a business close to the edge should stop dividing and build a month-by-month cash projection instead. The division is a summary that is only accurate when burn is flat, and burn is least flat exactly when the answer matters most.

Runway to zero versus runway to a milestone. Runway to zero is the date the money runs out. It is a useful alarm and a useless target, because arriving at zero having achieved nothing is the same outcome as arriving there early. The more decision-relevant question is whether the current cash reaches a specific event: profitability, the completion of a product, the start of a contract, the end of a seasonal trough, or the point at which the business becomes fundable. Framing it that way changes what a short runway means. Four months of cash is alarming in the abstract and unremarkable if the busy season starts in three.

It also changes the response. The three levers on runway are spending less, collecting faster, and adding cash, and they are not interchangeable. Cutting spending lengthens the runway and may push the milestone further away, which can make the position worse rather than better. Collecting faster raises the numerator without touching the milestone at all, which is why invoicing terms and collection discipline are usually the cheapest available lever.

The formal version of the same question. Auditors of public companies work to a standard that asks a structurally identical question with a fixed horizon. Public Company Accounting Oversight Board auditing standard AS 2415 requires the auditor "to evaluate whether there is substantial doubt about the entity's ability to continue as a going concern for a reasonable period of time, not to exceed one year beyond the date of the financial statements being audited." The conditions the standard lists as raising that doubt read like a description of a shortening runway: "recurring operating losses, working capital deficiencies, negative cash flows from operating activities, adverse key financial ratios", along with "default on loan or similar agreements" and "denial of usual trade credit from suppliers".

Two things follow for a small business, neither of which is a compliance obligation. One is that twelve months is a defensible answer to "how much runway is enough", because it is the horizon a formal standard settled on. The other is that the same standard is candid about the limits of the exercise: "The auditor is not responsible for predicting future conditions or events", and the absence of a going-concern reference "should not be viewed as providing assurance as to an entity's ability to continue as a going concern." A runway figure carries exactly the same caveat.

1. Establish available cash. Bank and operating balances, less anything already committed and about to leave, such as an imminent payroll or a tax deposit that has accrued.
2. Establish net monthly burn, averaged over enough months to smooth lumpy payments. Cash out less cash collected, excluding financing and owner transactions.
3. Divide. Cash divided by net monthly burn gives runway in months.
4. Decide which question you are answering. If a hiring plan, a price change or a seasonal shift is coming, replace the division with a month-by-month projection.
5. State any standby credit separately rather than folding an undrawn line into the numerator.
6. Name the milestone. Say what the runway has to reach, not just when it ends.

A hypothetical shows why a flat division understates a growing business. Halden Instruments holds $186,000 of cash. Over the last three months its cash out has averaged $61,000 and its collections have averaged $38,000, so its average net burn is $23,000 a month.

The snapshot answer is $186,000 ÷ $23,000 = 8.1 months.

Now suppose collections are growing by $4,000 a month, with spending flat. Net burn falls to $19,000 next month, $15,000 the month after, then $11,000, $7,000, $3,000, and turns negative in month six. Running the balance forward:

• Month 1: 186,000 − 19,000 = 167,000
• Month 2: 167,000 − 15,000 = 152,000
• Month 3: 152,000 − 11,000 = 141,000
• Month 4: 141,000 − 7,000 = 134,000
• Month 5: 134,000 − 3,000 = 131,000
• Month 6: collections exceed spending, and the balance starts rising

The business never runs out. Its snapshot runway of 8.1 months was not a slightly wrong estimate of its position; it was an answer to a different question, namely what would happen if growth stopped that day.

Reversing the assumption produces the mirror error. If collections instead fall by $4,000 a month, net burn rises to $27,000, then $31,000, $35,000, $39,000 and $43,000, and the balance runs 159,000, 128,000, 93,000, 54,000, 11,000. The $11,000 left after five months covers about a week at the sixth month's rate, so the business is out of cash early in month six rather than late in month eight. In both directions the snapshot is not an approximation of the answer; it is a different calculation.

Pros

• Converts a cash balance and a spending rate into a single number a decision can be made against, which neither input does on its own.
• Puts a date on the constraint, which is what turns "we should probably raise prices" into a scheduled decision.
• Cheap to compute and cheap to recompute, so it can be tracked monthly by a business with no finance staff.
• Frames the three available responses clearly, since spending less, collecting faster and adding cash are the only ways to move it.
• Read against a milestone rather than against zero, it says whether the current plan is actually financeable.

Cons

• It assumes a constant burn rate, which is the one thing a business under pressure or in growth reliably does not have.
• It inherits every ambiguity in the burn rate, including whether the figure was gross or net, so two runway numbers for the same business can differ by a factor of several.
• "Available cash" is a judgment, and including an undrawn credit line or excluding an imminent payroll changes the answer materially.
• It says nothing about whether the business is worth continuing. A long runway on an unprofitable operation buys time, not a solution.
• The number invites false precision. Eight-point-one months is arithmetic from three averages, and quoting the decimal implies a confidence the inputs do not support.