If you’ve ever tried to calculate startup runway by staring at your bank balance and doing rough math in your head, you already know the problem: it doesn’t give you a real answer. It gives you a guess dressed up as a number.
Runway isn’t your bank balance divided by a feeling. It’s a specific calculation, and once you know how to do it, you’ll never have to guess it again.
What Startup Runway Actually Measures
Runway is how many months your company can keep operating before you run out of cash, assuming nothing changes. It’s not a prediction of the future — it’s an honest read on your present. Runway anxiety is common and well-documented — SVB’s State of the Markets report has tracked how cash runway shifts across startups for years, and it moves more than most founders realize.
To calculate startup runway, you need two numbers: your current cash and your burn rate. Cash is easy — check your bank balance. Burn is where most founders go wrong, because there are two different ways to calculate it, and they answer two different questions.
Gross Burn vs. Net Burn
Gross burn is simply everything you spend in a month — payroll, software, rent, contractors, everything. It answers: “What does it cost to run this company?”
Net burn is what you spend minus what you bring in. It answers: “How fast is my cash actually shrinking?”
Here’s a simple example. Say your monthly expenses are $40,000 and your monthly revenue is $15,000.
If your bank balance is $200,000, your gross-burn runway looks like 5 months. But your real runway — the one based on net burn — is 8 months. Here’s what that looks like side by side:
That’s not a small difference. It’s the difference between “we need to cut costs this quarter” and “we have time to think clearly.”
Which Number Should You Use to Calculate Startup Runway?
Use net burn to know how much time you actually have. That’s your real runway number, and it’s the one to check regularly.
Use gross burn when you’re deciding what to cut. If you’re facing a cash crunch, gross burn shows you exactly where the money is going — line by line — so you know what’s actually movable.
Neither number replaces the other. Net burn tells you the size of the problem. Gross burn tells you where to look for the solution.
A Word of Caution on Revenue
If your revenue includes annual prepayments or upfront payments for contracts you haven’t fully delivered yet, be careful. That cash landed in your account, but it isn’t necessarily “earned” yet. Using it to lower your net burn can make your runway look longer than it really is. Say a chunk of this month’s revenue was actually an annual contract paid up front — your real net burn for this month is probably higher than the formula suggests. This is one of the most common ways SaaS founders end up surprised by their own numbers: the cash is real, but the timing is misleading.
What Happens When Revenue Isn’t Steady
The $15,000-a-month example above is clean because the revenue is flat. Most early-revenue SaaS companies aren’t that tidy — a big annual contract lands in March, a customer churns in April, a slow summer drags the numbers down. When revenue moves around, a single month’s net burn can be misleading in either direction.
Say your last three months of net burn looked like this: $10,000, $38,000, $22,000. The middle month had a customer churn and a slow renewal cycle; the first month had a large annual prepayment come in. If you calculate runway off any one of those months alone, you’ll get a wildly different answer depending on which month you happened to pick. Pick the $38,000 month and you’ll be halfway through drafting a very dramatic all-hands email before you realize it wasn’t actually that bad.
This is why the 3-month average matters more than it sounds like it should — a single month’s number can be misleading in either direction, but the average smooths that out.
That’s a number that’s still not perfect, but far more honest than any single month in isolation. If you want more confidence, look at 6 months instead of 3, especially if your revenue includes annual contracts that don’t repeat monthly.
How to Calculate Startup Runway, Step by Step
- Find your current cash. Your actual bank balance today, across all accounts.
- Calculate last month’s gross burn. Add up everything you spent — payroll, tools, rent, contractors, everything.
- Calculate last month’s net burn. Subtract last month’s actual revenue collected (being careful with prepayments, as above) from your gross burn.
- Divide. Cash ÷ net burn = runway in months.
- Repeat monthly. A single month’s burn can be noisy — a one-time expense, a slow sales month. Track it over 3 months and use the average for a more stable number.
Try It Yourself: Calculate Your Runway Right Now
Plug in your own numbers below — nothing is saved or sent anywhere, it all runs right here in your browser.
What to Do With Your Startup Runway Number
Now that you know how to calculate startup runway, the number by itself isn’t the goal — it’s a decision-making tool. Once you know it, you can ask sharper questions. Does this number give you room to hire, or should you hold? What does it mean for your timeline if you’re planning to raise? And which expenses are actually worth questioning? For a second opinion on any of these, that’s exactly what my services are built around.
If you calculate this once and it holds up, that’s a good sign. If you calculate it and the answer worries you, that’s useful information too — better to know now, with time to act, than to find out when the options have narrowed.
A Few Questions That Usually Come Up
Should I Use My Full Bank Balance, or Subtract Money I Already Owe?
If you have real near-term obligations sitting in that balance — taxes collected on behalf of others, a refund you already promised, money that’s technically someone else’s — subtract it first. Runway should reflect cash that’s actually yours to spend, not just whatever number the bank shows you.
What If My Burn Changes a Lot Month to Month?
That’s normal for an early-stage company, and it’s exactly why you recalculate monthly rather than treating one number as fixed. A single bad month doesn’t necessarily mean a new trend — but two or three months moving the same direction usually does.
Is There a “Good” Number of Months of Runway to Have?
There’s no universal answer, and be skeptical of anyone who gives you one without knowing your situation — how predictable your revenue is, whether you’re planning to raise, how fast you can adjust spending if you need to. What matters more than hitting a specific number is knowing your real number and checking it often enough that nothing about it surprises you.
If you’d rather have a second set of eyes confirm your runway and build out a full 13-week cash flow forecast, that’s exactly what my Cash Flow Clarity Audit does — a fixed $750, delivered in 7 business days, with a walkthrough call so you understand exactly what you’re looking at.
