What Is Runway and How Do You Calculate It

Yep, this is one of those numbers almost every founder thinks they have a handle on, right up until I ask for it out loud. Most founders I meet can tell me their bank balance to the dollar. Far fewer can tell me their runway to the week. That gap is the single most expensive blind spot I see, so let me close it for you, in plain language, with the formula, a real example, and the benchmarks that actually keep a company alive.

Here is the thing to understand up front, because it reframes everything that comes after. Runway is not an accounting term you file away in a spreadsheet and forget. It is a countdown clock. It is running right now, whether or not you are looking at it. And the whole job, mine when I am in your corner and yours every day, is to always know what the clock says and to never once be surprised by it.

So let me walk you through the mechanics, the one word inside the formula that fools smart people, what counts as healthy, when to start raising, and how to buy yourself more time when the clock gets short.

How you calculate runway

The math itself is not complicated, and I do not want to dress it up. Runway is your cash on hand divided by your net monthly burn. If you have $500,000 in the bank and you are burning $50,000 a month after revenue, you have ten months. That is the whole formula. Every serious source states it the same way, and Wall Street Prep puts it about as plainly as it can be put, that runway is "the amount of cash on hand divided by the burn rate."¹

The reason it matters is not the arithmetic, it is what the arithmetic tells you. Corporate Finance Institute describes runway as "the number of months a company can continue operating before it runs out of cash."² Read that again. Not how much you have, but how long you have. Those are two very different questions, and only one of them keeps the lights on.

Let me make it concrete, the way I would sketch it on a first call. Say you have $250,000 in the bank. You are spending $90,000 a month on payroll, rent, cloud, and tools, and you are bringing in $20,000 a month in revenue. Your net burn is $70,000, so your runway is $250,000 divided by $70,000, which comes out to about 3.6 months. That is Corporate Finance Institute's own worked example, and it is a sobering one.³ A founder staring at that $250,000 balance feels like they have room to breathe. A founder who knows they have 3.6 months of runway understands they have a decision to make this week, not next quarter.

One thing I will flag before we go further, because it trips people up quietly. Calculate your burn on a cash basis, meaning money that has actually landed in the bank, not invoices you have sent and not revenue your books have recognized. When we set up a young company at Island Waters, we often start it on a mostly cash basis for exactly this reason, then move to accrual once recurring revenue needs proper revenue recognition. It matters because the team at Kruze Consulting, who track hundreds of venture-backed startups, have found that incorrect expense categorization causes roughly a third of founders to miscalculate their burn by more than 15 percent.⁴ That is the difference between thinking you have a year and finding out, too late, that you had nine months.

The one word that fools everyone: net

This is the part I always slow down for, because it is where founders quietly mislead themselves and, worse, mislead their board. There are two burn numbers, and they are not the same animal.

Gross burn is everything you spend in a month, before a single dollar of revenue offsets it. Net burn is that number minus your revenue. The team at Mercury frames the split about as cleanly as anyone. Gross burn, they say, answers a worst-case question, "if all revenue stopped tomorrow, how fast would you go through your cash on hand?"⁵ Useful to know. But net burn is the one you live by, because it "tells you how quickly your cash balance is actually shrinking."⁶

That distinction is not academic, and the people who write the checks know it cold. Andreessen Horowitz, in their widely read piece on startup metrics, are blunt about which number an investor watches, noting that "investors tend to focus on net burn to understand how long the money you have left in the bank will last."⁷

So here is exactly how the trap springs. A founder tells me they have twelve months of runway. I ask how they got there, and it turns out they divided their cash by gross burn and then, on top of that, penciled in revenue from three deals that have not actually closed. Strip out the revenue that is not real yet, use net burn honestly, and that comfortable twelve months quietly becomes six. Carta's own numbers make the gap concrete. If your gross burn is $62,500 and you are generating $20,000 a month, your net burn is $42,500, and your runway has to be your cash divided by that figure, not by the bigger, friendlier one.⁸

Your bank balance tells you how much you have. Your net burn tells you how long you have. Only one of those keeps you alive, so when you say the word "burn" to a board or an investor, always say which one you mean.

What a healthy runway actually looks like

All right, so you can calculate the number honestly. What should the number be? The consensus across the investors I respect clusters tightly at 18 to 24 months, and it holds across stages. Bessemer Venture Partners frames the tiers about as simply as you could want in their State of the Cloud work: twelve months of runway is good, eighteen is better, twenty-four or more is best.⁹ NYU's Entrepreneurship Institute is just as direct, and I like that they do not hedge, telling founders to "target raising enough capital for 18 to 24 months of runway. This is not a random range."¹⁰

That guidance moved up after the 2022 reset, and it moved up for a simple reason: rounds started taking a lot longer to close. Ian Crosby, who founded Bench, argued in early 2023 that the floor should rise, that "you should be raising for a minimum of 18 months runway."¹¹ J.P. Morgan echoes the same caution, noting that in a tighter environment a more conservative 24 to 36 months is often the smarter target.¹² And the reason that caution is earned shows up plainly in Silicon Valley Bank's data. In its State of the Markets report covering the end of 2023, SVB warned that roughly half of US venture-backed startups would be out of cash within the year if they did not raise, and advised that a company raising its first round should secure at least nineteen months of cash.¹³

The clearest way I have ever seen this framed comes from Paul Graham of Y Combinator, and it has stuck with me for years. He built a single test every founder should be able to answer on the spot. Assuming your expenses hold steady and your revenue keeps growing the way it has, do you reach profitability on the money you have left? Or, as he puts it, "do they make it to profitability on the money they have left?"¹⁴ He calls the two states default alive and default dead, and the part that always gets me is his observation about "how often the founders themselves don't know."¹⁵

Graham also names the specific thing that quietly kills companies that just raised, and it is worth hearing straight from him: "Hiring too fast is by far the biggest killer of startups that raise money."¹⁶ I have watched that exact movie. A round closes, the whole team celebrates, and within ninety days the payroll line has doubled and the runway that looked like two years is suddenly fourteen months. Know your default state before you make the next hire, not after.

When to start raising, and why early beats late

Here is the timing mistake, and it is a genuinely costly one. Founders wait until runway is short to start raising, and by the time they pick up the phone they are negotiating from a position of weakness. A raise commonly takes three to six months from first meeting to money in the bank, and NYU lays the arithmetic right out: "It takes about 6 months to raise a round of capital."¹⁷ So if you only raised twelve months of cash, you are back on the road in six.

The honest rule is to start the process with nine to twelve months of runway still in the tank, and to never let it begin below about six months, because that is exactly where your leverage falls off a cliff. Mark Suster of Upfront Ventures boils down what he is really evaluating in a first meeting to three things, cash in, cash out, and milestones, and on the first two he is refreshingly plain: "Cash in is how much you're raising, cash out is how long your runway is."¹⁸ His companion advice, which I pass along constantly, is to meet investors long before you need a dime, so they watch your progress as a line instead of judging you on a single dot. Tell them you are not raising yet, he says, but that you will be in the next six months or so.¹⁹

When you raise from strength, with runway to spare, you set the terms of the conversation. When you raise on fumes, the market sets them for you, and that is how founders end up in down rounds and bridge rounds. This is not hypothetical. Carta's data showed down rounds hitting nearly 20 percent of deals at the end of 2023, roughly double the historical norm, and about 40 percent of 2024 seed rounds were bridges rather than fresh primary capital.²⁰²¹ A bridge can be the right call, but it is almost always a more expensive call than raising early would have been.

How to buy yourself more time

When the clock does get short, you are not out of moves. You have real levers, and here is roughly the order I reach for them, from the cleanest to the ones that need the most caution.

Cut burn, starting with headcount. Payroll dominates early-stage spending, so it is the biggest lever by a wide margin, and the least painful version is usually not layoffs. Tomasz Tunguz, who has looked at more startup financials than almost anyone, points to the gentler cut first, that "one of the best ways to reduce burn is to slow your sales hiring."²² Slowing the next few hires buys you months without gutting the team you have.

Grow revenue. This is the one everyone forgets to list as a runway lever, but every incremental dollar of real revenue lowers your net burn even if gross spending stays flat. It is the most capital-efficient way there is to extend the clock.

Tighten your working capital. Collect your receivables faster and stretch the non-critical payables. Pulling cash in sooner and pushing payments a little later widens the gap without cutting a thing, and it is often the fastest win sitting right in front of you.

Consider non-dilutive capital, but read the fine print. Venture debt can extend runway while keeping your cap table intact, which sounds like free money and is not. Kruze Consulting is refreshingly honest about the guardrails, warning that "taking on more than three to six months of runway in debt is usually excessive."²³ Debt adds a fixed repayment obligation and covenants, including material adverse change clauses that can let a lender call a default based on their read of your business, not just your bank balance.²⁴ Raise it from strength, as a supplement, never as a rescue.

And tie every dollar you spend to a milestone. I like NYU's discipline here, which is that if an expense does not get you closer to the milestone that triggers your next round, it gets cut.²⁵ That single question, does this move me toward the next raise, will clean up a budget faster than any spreadsheet exercise.

Once you actually have revenue, the conversation shifts from how long your cash lasts to how efficiently you are spending it, and investors will start judging that directly. David Sacks of Craft Ventures gave that judgment a name, the burn multiple, which is simply your net burn divided by your net new annual recurring revenue. The question it asks, in his words, is "how much is the startup burning in order to generate each incremental dollar of ARR?"²⁶ His rough scale runs from amazing under 1x to bad above 3x, and he likes it because he calls it "a catch-all metric" that eventually reflects any serious problem in the business.²⁷²⁸ For a SaaS or AI company nearing scale, the Rule of 40 is the companion frame, your growth rate plus your profit margin clearing 40 percent, which is really a way of asking how much burn your growth actually earns you.²⁹

The cautionary tale I would rather you hear from me

The most vivid runway failure I can point to is Quibi. The short-form video app raised about $1.75 billion, an amount most founders cannot even picture, launched in April 2020, and shut down roughly six months later. In their farewell letter, cofounders Jeffrey Katzenberg and Meg Whitman were candid that the idea itself may not have justified a standalone service in the first place.³⁰

Here is why I tell that story, though, and it is not the punchline you might expect. The lesson is not that Quibi ran out of money. The lesson is that running out of money is almost always the symptom, not the disease. CB Insights, after analyzing hundreds of recent startup shutdowns, found that running out of capital tops the list at about 70 percent, but described it as almost always the final cause of death rather than the root problem, which is usually weak product-market fit underneath.³¹ Runway buys you the time to go find product-market fit. It does not, and cannot, substitute for it. So knowing your number precisely is not the goal in itself. It is the thing that gives you enough runway to solve the real problem before the clock hits zero.

That is really the whole point of this work. Not to admire a metric, but to move the moment of discovery from six weeks out to six months out, back when you still have options and choices instead of a fire drill.