How to Calculate Runway and Burn: Gross vs Net, and the Mistakes Founders Make
Runway and burn are the two numbers that tell you how long your company gets to keep operating before it needs more cash. Burn is how fast money leaves the account. Runway is how many months of it you have left. Every other metric a startup tracks assumes the company is still alive to track it, which is why these two sit at the top of the list.
The math looks simple, and that is the trap. Founders get burned by the definitions more than the arithmetic: gross burn versus net burn, a raw bank balance that hides committed spend, a one-time inflow that flatters a month. This guide gives you precise definitions, a worked example with real figures, the specific mistakes that make the number lie, and how often to recompute it as your company grows.
Gross Burn, Net Burn, and Runway, Defined
Start with clean definitions, because most bad runway numbers come from mixing these up. The U.S. Securities and Exchange Commission describes burn rate as the pace at which a new company uses up its cash, and warns that a company burning cash faster than planned can run out before it turns a profit. See SEC, Investor.gov: Burn Rate for the primary reference.
Gross burn: the total cash that leaves the business in a month. Payroll, rent, software, contractors, hosting, taxes, every dollar out, before you count a single dollar coming in. Gross burn measures the size of your cost base regardless of revenue.
Net burn: cash out minus cash in. If you spend $250,000 and collect $100,000, your net burn is $150,000. Net burn is the number that actually drains the bank account, because revenue offsets part of the spend. The Corporate Finance Institute defines net burn the same way, as operating expenses minus revenue over a month.
Runway: how many months you can keep going at the current pace, calculated as cash on hand divided by monthly net burn. With $1,200,000 in the bank and $150,000 of net burn a month, runway is eight months. Runway is expressed in months for a reason: it maps directly onto how long until you have to raise, cut, or reach profitability.
One rule holds the whole thing together. Runway is almost always calculated on net burn, not gross, because revenue really does slow the drain. Gross burn tells you how heavy your cost base is; net burn tells you how long you last. Track both, and never quote a runway number without saying which burn it sits on top of.
A Worked Example, Start to Finish
Numbers make this concrete. Suppose it is the last day of the month and you sit down to compute the two figures for a seed-stage company.
You have $1,200,000 across your accounts. Over the month, $250,000 in cash went out the door: $170,000 of payroll and benefits, $30,000 of software and hosting, $25,000 of rent and facilities, and $25,000 of contractors and everything else. That $250,000 is your gross burn.
Over the same month you collected $100,000 from customers. Subtract that from the $250,000 that left, and your net burn is $150,000. That is the amount your bank balance actually fell by, assuming no financing or one-time items.
Now the runway. Divide cash by net burn: $1,200,000 divided by $150,000 is eight months. If you ran the same division on gross burn, $1,200,000 divided by $250,000, you would get 4.8 months, which is the answer to a different question: how long you would last if revenue vanished tomorrow. Both are worth knowing. Here is the full calculation in one view.
Here is the same example as a quick recap:
Cash balance today: $1,200,000
Monthly gross burn, all cash out: $250,000
Monthly revenue collected: $100,000
Monthly net burn, out minus in: $150,000
Gross runway, cash divided by gross burn: 4.8 months
Net runway, cash divided by net burn: 8 months
Eight months is the headline number, and it is the one that should drive your fundraising calendar. The 4.8-month gross figure is a stress test: it tells you how exposed you are if a big customer churns or a contract slips.
The Mistakes Founders Make
The arithmetic above takes two minutes. The reason founders still get runway wrong is that the inputs are easy to corrupt. These are the errors that show up again and again.
Confusing gross and net burn: quoting gross burn as if it were net, or the reverse, throws the runway off by a wide margin. In the example, the same company is either eight months or 4.8 months from empty depending on which burn you use. Pick a net for the runway, and label it every time.
Letting a one-time inflow hide the true burn: a tax refund, a grant, a deposit return, or a chunk of prepaid annual revenue lands in one month and makes net burn look tiny or even negative. If you compute the runway off that single flattered month, you will badly overstate how long you have. Strip one-time items out and look at burn on a normal operating month, or average over three months.
Using the raw cash balance without deducting committed spend: the number in the account is not all spendable. A signed lease, an annual software contract you have committed to, a bonus pool you owe, taxes you have collected but not remitted: that money is spoken for. Subtract known committed outflows before you call it cash on hand, or your runway will read longer than it is.
Ignoring the timing of receivables and payables: cash accounting and the calendar do not always agree. If a large customer payment is booked as revenue but has not landed, or a stack of vendor bills is due next week, the timing of accounts receivable and accounts payable can swing a single month's net burn hard. Look at when cash actually moves, not just when an invoice was issued.
Not adjusting for a known upcoming change: burn is a forecast, not just a record. If you are about to close two senior hires or sign a bigger office lease, next quarter's burn is higher than last month's, and your real runway is shorter than the trailing number says. Build the known change into a forward burn figure before you decide you have plenty of time.
How Often to Recompute, and What Healthy Runway Looks Like
Recompute burn and runway at least monthly, right after the books close for the month, so the figure sits on real settled numbers. Many founders also glance at a rough version weekly, especially inside the last six months of runway, when the pace of decisions picks up. The closer you are to zero, the more often the number should be in front of you.
What counts as healthy depends on the stage. The rough convention among investors is to raise enough for eighteen to twenty-four months of runway at each round, then spend the middle of that window building toward the metrics the next round requires and the last few months raising. That means a healthy runway is not a fixed number of months; it is enough time to hit the milestone that unlocks the next check plus a buffer to raise it.
Early stage: a pre-seed or seed company usually wants a longer cushion, because revenue is small and unpredictable and the next round depends on proof that takes time. Here net burn and gross burn are close together, so watch the cost base directly.
Growth stage: as revenue climbs, net burn falls below gross burn and can approach zero. Runway math shifts from survival to efficiency, and metrics like net burn against net new revenue start to matter as much as the month count.
Whatever the stage, the trigger to act is time, not mood. If you are inside the window where raising your next round would take longer than your remaining runway, you are already late. Working backward from that point is the entire reason to keep the number current.
Keeping the Inputs Current
A runway number is only as good as the three inputs behind it: the balance across every account, the cash coming in, and the cash going out. The work is not the division; it is keeping those inputs fresh and complete, especially when money is spread across several accounts and entities.
Balances: pull the current cash across every operating account, reserve account, and entity, and add them up as one figure. A balance you checked three weeks ago is already stale for a weekly read.
Inflows: capture what actually landed from customers this period, and flag anything one-time so it does not distort the trend. Revenue you invoiced but have not collected is not cash yet.
Outflows: total every category of spend, including the committed items that have not cleared, so gross burn reflects the real cost base rather than only what happened to post.
Meow keeps these inputs in one place. Business checking, corporate cards, treasury, and multiple entities sit under a single login with a multi-entity dashboard, so the balance, inflow, and outflow figures you need for the calculation come from one source instead of a spreadsheet stitched together from five bank portals. When the inputs are current and consolidated, recomputing the runway is a two-minute habit rather than a monthly project.
Frequently Asked Questions
What is the difference between gross burn and net burn? Gross burn is the total cash that leaves the business in a month, before counting any revenue. Net burn is cash out minus cash in over the same month. If you spend $250,000 and collect $100,000, gross burn is $250,000 and net burn is $150,000. Runway is almost always calculated on net burn, because revenue offsets part of the spend.
How do you calculate the runway? Divide your current cash by your monthly net burn. With $1,200,000 in cash and $150,000 of net burn a month, runway is eight months. Use net burn rather than gross burn so the figure reflects the fact that revenue slows the drain, and subtract any committed spend from the cash balance first.
How much runway should a startup have? A common convention is to raise enough for eighteen to twenty-four months at each round, spend the middle building toward the next round's milestones, and use the final months to raise. A healthy runway is enough time to hit the milestone that unlocks the next round plus a buffer to close it, so the right number depends on your stage and how long a raise takes.
How often should I recalculate burn and runway? Recompute at least monthly, right after the books close, so the number rests on settled figures. Many founders also check a rough version weekly, especially inside the last six months of runway when decisions come faster. The closer you are to zero, the more often you should look.
Why does a one-time inflow distort the runway? A tax refund, a grant, or a slug of prepaid annual revenue lands in one month and makes that month's net burn look small or even negative. Runway computed off that flattered month overstates how long you have. Strip one-time items out and use a normal operating month, or average over three months.
Should I use the raw bank balance as my cash on hand? No. The number in the account includes money that is already committed: a signed lease, an annual contract, a bonus pool, taxes collected but not yet remitted. Subtract known committed outflows before calling it cash on hand, or your runway will read longer than it really is.
A Note on Meow
The hardest part of runway math is not the formula, it is assembling clean inputs from accounts that live in different places. Meow is built so the balance, the inflows, and the outflows sit under one login. Business checking, corporate cards, and treasury share the same view, and funds and management entities can be onboarded together on the multi-entity dashboard. That is by design: the point of consolidating money movement is that the numbers you need to run the business are already in one place when you sit down to compute them.
The Bottom Line
Runway and burn reward precision. Separate gross from net, put runway on net burn, strip out one-time inflows, deduct committed spend, and adjust for the hire or contract you already know is coming. Recompute it monthly, watch it weekly when the window gets short, and keep the inputs current across every account. Open an account at meow.com.
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