Runway, burn multiple, and default alive versus default dead are three numbers every founder should be able to recite without opening a spreadsheet.
You need to know how to calculate startup runway before your board asks, not after your accountant flags it. The math is short. The consequences of ignoring it are not.
Runway is simply the number of months your company can survive at its current spending pace before the bank account hits zero. Take your cash in the bank, divide it by your net monthly burn, and you have your answer. If you're sitting on $2.4 million and losing $150,000 a month after revenue, you have sixteen months. That's it. No adjustment for optimism, no credit for the deal that's "about to close."
Net burn is the number that trips founders up. It's not your total spending. It's total cash out minus cash in, meaning payroll, rent, software, and everything else, minus whatever revenue you're actually collecting that month. A company spending $400,000 a month with $250,000 in monthly recurring revenue has a net burn of $150,000, not $400,000. Confuse gross and net burn and you'll either panic early or, worse, run out of runway while still telling investors you have a year left.
Gross burn matters too, just for a different question. It tells you the size of the cost base you'd have to cut if revenue disappeared tomorrow. A founder who only ever quotes net burn to the board is, whether they mean to or not, hiding how exposed the company actually is to a revenue slowdown. Track both numbers side by side. Gross burn shows your fixed commitment. Net burn shows your actual monthly cash loss. Runway is calculated from the second, but the first tells you how fast that second number could get worse.
Plenty of spreadsheet templates and cash runway calculator tools will spit out a months-remaining number for you. They're fine for a snapshot. But a static runway number lies by omission, because it assumes your burn rate stays flat. It rarely does. Headcount grows, marketing spend gets approved, office leases renew at higher rates. The founders who get blindsided aren't the ones who can't do division. They're the ones who calculated runway once in January and never touched the model again.
Basecamp, back when it still operated as a bootstrapped software company before its restructuring into 37signals, became something of a case study in the opposite discipline: obsessive, monthly tracking of revenue against cost, with no fundraising cushion to hide behind. Jason Fried has said publicly that the company never took outside capital specifically because it forces exactly this kind of runway math to matter every single month, not once a quarter for a board deck. Most venture-backed startups don't have that luxury of discipline built in by necessity. They have to build the habit on purpose.
Update your burn number monthly, not quarterly. Rebuild your runway forecast every time headcount changes. And separate your runway from your fundraising runway, which is shorter: investors want to see six or more months of cash left when you start a raise, not two, because a two-month clock during due diligence is visible to every VC in the room and it shows.
The burn multiple tells you if that spending is working
Runway tells you how long you have. It says nothing about whether the money is being spent well. That's what the burn multiple is for.
David Sacks, the former PayPal COO and Craft Ventures partner, popularized the metric in a widely shared 2022 memo as SaaS valuations collapsed and growth-at-any-cost stopped being fundable. The formula: net burn divided by net new annualized recurring revenue. Burn $2 million in a quarter and add $1 million in new ARR, and your burn multiple is 2. Sacks' bands, since adopted across the venture industry, run roughly like this: below 1 is amazing, 1 to 1.5 is great, 1.5 to 2 is good, 2 to 3 is suspect, and anything above 3 is bad.
Here's why this matters more than growth rate alone. A company growing revenue 150% a year sounds unstoppable until you learn it's burning $5 for every $1 of new ARR. That's a company renting its growth, not earning it, and the moment capital gets expensive, the model breaks. The burn multiple exposes that in one number, which is exactly why it spread so fast among operators after Sacks published it. It's the ratio that turns "we're growing fast" into "we're growing efficiently," and those are not the same claim.
Founders should calculate it quarterly, not as a vanity metric for the pitch deck, but as an internal check on whether the last dollar spent bought a dollar of durable revenue or just bought time. If your burn multiple is climbing quarter over quarter while your growth rate stays flat, that's the earliest warning sign you'll get, and it shows up months before the cash balance itself looks alarming.
Default alive vs default dead, and why the label changes your decisions
Paul Graham drew this distinction in a 2015 essay that's still the clearest framing available: a startup is default alive if, at its current growth rate and expense trajectory, it reaches profitability before the money runs out. It's default dead if it doesn't, meaning it needs another round of funding just to survive, regardless of how good the product is.
The distinction matters because it changes what a founder should actually be doing. A default dead company that thinks it's default alive keeps hiring, keeps spending on growth experiments, and keeps telling itself the next round will materialize on the current timeline. Graham's warning was blunt: default dead companies that don't recognize their own status often die not because they couldn't have survived, but because they didn't cut spending in time to become default alive while they still had the runway to do it.
Run the test honestly. Take your current revenue growth rate, apply it forward, and ask whether expenses hit breakeven before cash hits zero, assuming no new funding arrives at all. If the answer is no, you're default dead, and the only two ways out are cutting burn or raising capital on a timeline you don't control. Neither is comfortable. Both are better than finding out during a term sheet negotiation that already reflects your desperation.
Put the numbers together before the gap, not during it
Fundraising gaps are where this math actually gets tested. The market environment since 2022 stretched the average time between rounds for venture-backed startups well past the twelve to eighteen months founders used to plan around, and a lot of companies that raised comfortably in 2021 found themselves calculating runway for the first time under real pressure in 2023 and 2024.
Do the arithmetic now, while it's just a number on a spreadsheet and not a deadline pressing on every hiring decision. Calculate your months of runway from cash and net burn. Calculate your burn multiple from net burn against net new ARR. Run the default alive test against your actual growth curve, not the one in last year's projections. Three numbers, updated monthly, and you'll know exactly where you stand before an investor has to tell you.
Also read: How to Build a 30 60 90 Day Plan Template for a New Startup Hire • How to Structure Founder Vesting When You Bootstrap Then Raise Later • How Much Salary Should a Startup Founder Pay Themselves at Each Stage
