Runway and Burn Rate: The Two Numbers Founders Should Always Know

Two numbers describe the financial position of an early company more usefully than any others. Burn rate is how fast you are consuming cash. Runway is how long that leaves you. Founders who cannot state both without checking are usually about to be surprised by one of them.

Gross and Net Burn Are Different

Gross burn is total monthly cash out. Net burn is cash out minus cash in — what the balance actually falls by each month. Both are worth knowing: net burn tells you how long you have, while gross burn tells you the size of the operation you are running regardless of revenue.

A business with high gross burn largely covered by revenue is in a different position from one with the same net burn and no income, because the first has something that can be scaled back and the second does not.

Calculating Runway

Divide the cash you hold by net monthly burn. The result is the number of months before the money is gone at the current rate. It is a simple calculation that most founders perform less often than they should, and the value is in updating it monthly rather than in its precision.

Use Realistic Assumptions, Not Hopeful Ones

Runway calculated on expected revenue rather than committed revenue overstates how long you have. Calculate it twice: once with contracted income only, and once with your realistic forecast. The first number is the one that determines when you must act. A cash flow forecasting model makes this straightforward to maintain.

Twelve to Eighteen Months Is the Usual Target

Rounds are typically sized to fund a period long enough to reach a meaningful milestone with margin for it taking longer. Raising for six months means starting the next raise almost immediately, from a weak position, before there is anything new to show.

Fundraising Consumes Runway While It Happens

A raise takes months, and the burn continues throughout. Beginning with three months of runway means running out during the process, which removes your ability to decline poor terms — and experienced investors recognise that position immediately. Whether raising from angel investors or institutionally, start while saying no is still available.

Burn Per Milestone Is More Useful Than Burn Per Month

A monthly figure tells you the rate. What actually matters is how much cash it takes to reach the next thing that changes the company’s position — a working product, a certain level of revenue, a regulatory approval. Expressing burn that way turns it from a number you monitor into a number you can act on.

Watch the Trend, Not the Single Month

One expensive month with an annual payment in it is not a change in burn rate. Look at a rolling three-month average to see the underlying direction, and separate one-off costs from recurring ones. Reacting to a single month produces decisions that get reversed the following one.

Extending Runway Without Raising

Every month of runway added is a month of leverage. Reducing discretionary spend, renegotiating supplier terms, invoicing sooner, taking deposits, and slowing hiring all extend it. So does raising prices, which is usually the fastest lever and the one founders reach for last.

Recalculate After Any Significant Change

A new hire, a lost customer, a price rise or a large purchase all move both numbers. Update them at the point of the decision rather than at the next month end, because the purpose of the figures is to inform the decision rather than to describe it afterwards.

Cutting Late Is Worse Than Cutting Early

Reductions made with nine months of runway can be measured and reversible. The same reductions made with two months are forced, deeper than necessary, and damaging to the business you are trying to save. If the numbers say a decision is coming, making it early is almost always cheaper.

Burn Is Not Automatically Bad

Spending ahead of revenue is the point of taking investment, and a company burning cash to build something valuable is doing what it raised money to do. The question is whether the spending is buying progress towards a defined milestone. Burn without a milestone is simply the business getting smaller more slowly than it appears.

Measure Burn on Cash, Not on Accounts

Burn is a cash figure, so it must be calculated from money actually leaving the bank rather than from accounting costs. Depreciation reduces reported profit without touching cash; a large annual insurance payment hits cash without affecting the monthly profit and loss. Calculating burn from the profit figure produces a number that does not describe your position.

Tie Runway to a Milestone, Not a Date

The useful question is not how many months remain but whether they are enough to reach the point that makes the next raise possible. Runway measured against a milestone tells you whether the plan works. Runway measured against the calendar only tells you when it stops.

Know Whether You Are Default Alive

A useful test is whether the company reaches profitability on its current trajectory before the money runs out, assuming no further funding. If it does, you are negotiating from strength because you do not strictly need investors. If it does not, you are dependent on raising, and that changes what terms you can realistically decline.

Distinguish Committed Costs From Discretionary Ones

Some of your burn can be stopped quickly and some cannot. Property leases, employment contracts and long service agreements are committed; marketing spend and contractors usually are not. Knowing the split tells you how much of the burn you could actually remove in a difficult month, which is the number that matters in a crisis.

Be Straight With the Team

Founders often conceal a shortening runway to avoid alarming staff, and the effect is usually the opposite of what is intended — people sense the change and imagine something worse. Senior staff in particular make better decisions about hiring and commitments when they know the actual position.

Report Both to Whoever Is Watching

Investors expect these figures in updates, and lenders assessing you will ask. Knowing them without checking signals control of the business, which affects how the rest of your numbers are received. It is also the fastest way to establish credibility when discussing further startup capital.