A Founder’s Survival Metric: How To Calculate Cash Runway Accurately
Your cash runway isn’t just a metric; it’s the master clock of your startup. Understand how to calculate it, what it signals to investors, and how to use it to make critical decisions before you run out of time.
TL;DR: Calculating your cash runway (Cash Balance ÷ Net Monthly Burn) is a critical founder skill. A simple calculation is often misleading; you must account for all one-off and recurring expenses, model multiple scenarios (baseline, conservative, aggressive), and understand what your runway number signals to investors. Use your runway to create a fundraising calendar and make strategic decisions long before you’re in the danger zone (less than 6 months of runway).
Key takeaways
- Calculate runway using Net Burn (Total Cash Out - Total Cash In), not just expenses.
- Don't trust a single number; model at least three scenarios for your runway.
- Your runway dictates your fundraising timeline. Start the process with 9-12 months of cash left.
- Avoid common traps like forgetting annual bills or confusing revenue with cash-in-hand.
- Look at your runway every month. It’s a health metric, not a one-time calculation.
- A runway over 18 months signals strength; under 6 months is a five-alarm fire.
Your Runway Isn’t a Metric, It’s Your Master Clock
Cash runway isn’t an accounting exercise. It’s the single most important number dictating your startup’s life or death. It’s the countdown clock that determines your strategic options, your leverage with investors, and your ability to sleep at night.
Knowing your runway isn’t about filling out a spreadsheet. It’s about understanding exactly how much time you have to build a company that can either sustain itself or convince others to fund its growth. Getting this wrong is a fatal, unforced error. Here’s how to get it right.
The Basic Formula (and Why It’s Dangerously Simple)
At its core, the runway calculation looks straightforward:
Cash Runway (in months) = Current Cash Balance / Net Monthly Burn
The problem is, founders often get both parts of this equation wrong. "Current Cash Balance" can be fuzzier than it looks, and "Net Monthly Burn" is a minefield of potential miscalculations.
Let's break down how to calculate this with the precision it deserves.
Step 1: Nail Down Your True Cash Balance
This should be the easiest part, but founders still trip up. Your cash balance is the money that is actually in your bank account right now, plus any funds you can access within 30 days. This includes:
- Cash in checking/savings accounts: The obvious starting point.
- Committed, wired funds: Money from an investment that has been signed and is pending transfer. Do not count verbal commitments.
What it does not include:
- Accounts Receivable (AR): A customer owes you $50,000. That isn't cash until it's in the bank. Don’t count it in your cash balance.
- Investor promises: A "soft circle" is not cash. A signed term sheet is not cash. Only a signed SAFE/Priced Round agreement with a specific wire date is close enough to consider.
Step 2: Calculate Your Real Net Burn
This is where most mistakes happen. Your burn rate isn’t just your list of monthly expenses. It’s the net cash flow of the entire business.
There are two types of burn:
- Gross Burn: Your total monthly cash expenses. This shows your total spending footprint.
- Net Burn: Your total monthly cash expenses minus any cash revenue you collect that month. This is the number that matters for runway.
Continue reading the full guide
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