Burn Rate and Runway: How Startups Measure the Time They Have

Gross burn and net burn

Burn rate is the speed at which a company uses its cash, usually expressed per month. Gross burn is the total spent in a month: salaries, rent, software, advertising, suppliers and everything else. Net burn is gross burn minus the cash that came in from customers in the same month.

Net burn is the figure most people mean when they talk about burn rate, because it describes how much the cash balance actually shrinks. A company with high gross burn and strong sales may have modest net burn; a company with lower costs and almost no revenue may burn more in net terms.

Burn is measured in cash, not in accounting profit. A large customer that pays a year in advance raises cash today, while a supplier invoice paid late delays an outflow. Both change the burn picture even if the underlying business has not changed.

Runway: months until the cash runs out

Runway is the number of months a company can continue at its current net burn before it runs out of cash. The basic calculation divides the cash in the bank by the monthly net burn. A company with enough cash to cover twelve months of net burn has, on paper, a year of runway.

The calculation is simple, and that simplicity hides several assumptions. It assumes burn will stay the same, that revenue will not fall, that no large unexpected cost appears and that the company can actually use all the cash, rather than having part of it committed elsewhere.

Why runway sets the calendar for fundraising

Raising money from investors usually takes months: preparing materials, meeting potential investors, negotiating terms and completing legal work. A company that begins this process with little runway left negotiates from a weak position, because investors know it cannot wait.

For this reason, founders often plan to start raising well before runway becomes short. Many also plan each round of funding around specific milestones, such as a level of revenue, a product launch or proof that customers stay, which they expect to reach before the cash runs low. If the milestone is reached, the next round should be easier; if not, the company may have to raise on worse terms or not at all.

Funding conditions also change. In some years investors compete to fund startups; in others they become selective. Runway that seemed comfortable when money was easy to raise can prove short when it is not.

The levers a company can pull

A company with shrinking runway has a limited set of options. It can raise more money, from existing or new investors, sometimes on less favourable terms. It can reduce costs, which usually means fewer hires, smaller marketing budgets or layoffs. It can try to increase revenue faster, for example by raising prices or focusing on its most profitable customers.

Some companies borrow, through venture debt or other loans, to extend runway. Borrowing adds repayment obligations and interest, so it changes the risk rather than removing it. Others look for a buyer, merge with another company or, when none of these work, close.

The aim of many founders is to reach a point where revenue covers costs, sometimes called default alive: if nothing else changed, the company would survive on its own income. A company that would run out of cash under the same conditions is described as default dead.

Why the estimate is never firm

Runway is often quoted to the month, which gives it an air of precision. In practice it is a forecast built on assumptions about costs and revenue that can change quickly. A key customer leaving, a delayed product or a sudden rise in costs can shorten runway by months.

Careful founders usually calculate several versions: one at current burn, one assuming planned hiring, and one with lower revenue than expected. The gap between those versions is a more honest picture of the situation than a single figure.

Timing adds another layer. Cash rarely leaves at an even pace: annual software contracts, tax payments and hiring plans can create months of much higher burn. A runway figure based on an unusually quiet month can therefore overstate the time available.

What this means for people who invest in startups

For anyone who has invested in a young private company, or is considering it, burn rate and runway are central to understanding the risk. A company with a short runway and no clear path to more funding may need to raise money on terms that reduce the value of existing shares, or may fail entirely, in which case shareholders can lose all of their investment.

Shares in private companies are also hard to sell before a sale of the company or a public listing, so investors may not be able to exit if the outlook changes. This article is general education and is not a recommendation about any investment.