How to Calculate Your Startup's Burn Rate (And Why It Matters)

Every startup that has ever died ran out of money. That's not a philosophical statement — it's a mechanical one. And the tool that tells you exactly when that will happen is your burn rate. Despite being the single most important financial metric for a pre-profit startup, most first-time founders calculate it wrong, monitor it inconsistently, or ignore it entirely until the bank balance triggers a panic.

Gross Burn vs. Net Burn: They're Not the Same Thing

Gross burn is the total amount of money your company spends each month. Every dollar out the door — salaries, rent, AWS bills, software subscriptions, that fancy espresso machine for the office. If you spend $150,000 per month in total, your gross burn is $150K/month.

Net burn is your total spending minus your revenue. If you spend $150,000 per month but bring in $40,000 in revenue, your net burn is $110,000 per month. This is the number that actually determines your runway.

The distinction matters because they tell you different things. Gross burn reveals your cost structure and operating leverage. Net burn tells you how quickly you're consuming your cash reserves. When investors ask about your burn rate, they almost always mean net burn. When you're thinking about cuts, you need to look at gross burn line by line.

How to Calculate Your Actual Runway

The basic runway formula is simple: Cash in bank divided by monthly net burn equals months of runway. If you have $1.2 million in the bank and your net burn is $100,000/month, you have 12 months of runway.

But this static calculation is dangerously misleading for three reasons. First, your burn rate isn't constant. You're probably hiring, which means burn increases over time. Second, revenue might be growing, which reduces net burn. Third, one-time expenses (annual contracts, equipment purchases, security deposits) create spikes that a monthly average smooths over.

A better approach: build a forward-looking cash model. Project your expenses month by month for the next 18 months, factoring in planned hires and known cost increases. Layer in your revenue projections (use conservative estimates). The month where your cumulative cash hits zero is your real runway deadline. Update this model every month.

The "Default Alive" Framework

Paul Graham introduced a powerful mental model: are you default alive or default dead? Default alive means that if your revenue keeps growing at its current rate and your expenses stay flat, you'll reach profitability before running out of money. Default dead means you won't — you'll need to raise more money or cut costs to survive.

This is the single most important question a founder can answer at any given time. If you're default alive, you have leverage. You can raise from a position of strength, negotiate better terms, or choose not to raise at all. If you're default dead, every month that passes without either accelerating revenue growth or reducing burn is a month closer to an existential crisis.

To calculate this: take your current monthly revenue growth rate, project it forward with compounding, and plot it against your expense trajectory. Where those two lines cross is your break-even point. If it happens before you run out of cash, you're default alive.

What "Good" Burn Looks Like at Each Stage

Pre-seed and seed stage: $30,000-$80,000/month is typical. You should be spending almost entirely on product and engineering. If your burn is over $100K/month and you haven't found product-market fit, something is wrong. Aim for 18-24 months of runway.

Series A: $150,000-$400,000/month. You're scaling the team, maybe adding sales and marketing. The critical thing is that burn should be increasing because you're investing in proven channels, not because you're experimenting expensively. Target 18-24 months of runway post-close.

Series B and beyond: $500,000-$2,000,000+/month. At this stage, the absolute number matters less than the ratio. A common benchmark is the "burn multiple" — net burn divided by net new ARR. A burn multiple under 2x is excellent. Between 2x and 4x is acceptable. Above 4x means you're spending too much for the growth you're getting.

When to Cut vs. When to Raise

The rule of thumb: start fundraising when you have 9-12 months of runway remaining. Fundraising typically takes 3-6 months for Series A and beyond, and you want to close with at least 6 months of cash in reserve. That means if your runway drops below 9 months without a fundraise in progress, you should be concerned.

When should you cut instead of raise? Three scenarios. First, if you're not growing fast enough to justify a new round — investors will pass, and the fundraise will burn time and morale. Second, if the market is in a downturn and valuations are compressed — raising at a down round can be more damaging than a strategic reduction. Third, if you can reach profitability or near-profitability with modest cuts — that's almost always the better path.

The biggest mistake founders make is cutting too little, too late. If you need to cut, cut once and cut deep enough that the problem is solved. Rolling layoffs in small batches destroy team morale far more than a single painful restructuring.

Monitoring: The Dashboard You Actually Need

Set up a monthly financial review with these five numbers: cash balance (check your bank, not your accounting software), gross burn (total expenses), net burn (expenses minus revenue), runway in months (cash divided by net burn), and default alive status (yes or no, based on growth trajectory).

Track these in a spreadsheet, update them on the first of every month, and share them with your co-founders and board. The founders who get blindsided by cash crunches are the ones who don't look at these numbers regularly. The founders who navigate them successfully are the ones who see problems six months before they become emergencies.

Your burn rate isn't just a number — it's a countdown. Know exactly where it stands, what's driving it, and what levers you have to change it. That awareness is the difference between running out of money and running a company.