Burn Rate, Runway & Cash Flow: The 3 Numbers Every Founder Must Know
1. Burn Rate — How Fast Are You Spending?
Burn rate is the amount of cash your startup spends every month. There are two versions, and you need to know both.
Gross Burn
Total cash out the door every month — salaries, rent, software, contractors, marketing, everything.
Formula: Total monthly expenses = Gross Burn
Net Burn
Gross burn minus any revenue you’re generating. This is the number that actually matters for runway calculation.
Formula: Monthly expenses − Monthly revenue = Net Burn
Example: Monthly expenses of $120,000 minus monthly revenue of $35,000 = Net burn of $85,000
Context matters: Rising burn with flat revenue is a warning sign. Rising burn with rising revenue at improving margins is a growth signal. The number itself means nothing without the context of what’s driving it.
2. Runway — How Much Time Do You Have?
Runway is the number of months your startup can operate before running out of cash at your current burn rate. It is the single most important number for timing your next fundraise.
Formula: Cash on hand ÷ Net monthly burn = Months of Runway
Example: $850,000 in the bank ÷ $85,000 net burn = 10 months of runway
Most experienced investors recommend starting your fundraise when you have 6–8 months of runway remaining — not when you’re down to 2 months. Raising from urgency almost always results in worse terms. Raising from runway gives you leverage.
The practical implication: If your runway calculation says 10 months, you should be thinking about your next raise right now.
Critical mistake: Calculating runway based on current cash without accounting for upcoming large expenses — a key hire, a marketing campaign, an annual software renewal. Always run a forward cash flow forecast alongside runway to catch these before they hit.
3. Cash Flow — Where Is the Money Actually Going?
Cash flow is the movement of money into and out of your business over time. Unlike burn rate (a monthly snapshot) and runway (a forward projection), cash flow shows you the full picture — when money arrives, when it leaves, and what the net effect is on your bank balance.
The tool that makes cash flow actionable is a 13-week cash flow forecast — a rolling, week-by-week projection of every dollar coming in and going out for the next 13 weeks. It tracks:
- Expected customer payments and when they’ll actually clear
- Payroll dates and amounts
- Vendor payments and timing
- Tax payments and quarterly estimates
- Large one-time expenses
Most startups that run out of cash don’t run out suddenly. They run out predictably — they just weren’t looking far enough ahead to see it coming.
How These Three Numbers Work Together
Burn rate tells you the speed. Runway tells you the distance. Cash flow tells you the terrain.
A startup with $100,000 net burn and 12 months of runway looks healthy. But if the cash flow forecast shows three large vendor payments hitting the same week as payroll in month 3 — creating a temporary shortfall — that’s a problem to solve now, not in month 3.
These three numbers don’t exist in isolation. They need to be reviewed together, updated regularly, and used actively to make decisions — about hiring timing, fundraising timing, marketing spend, and operational efficiency.
The founders who know these numbers cold — without opening a spreadsheet — make better decisions faster, raise money from strength, and build companies that survive long enough to succeed. Start tracking them weekly. It takes 20 minutes and changes everything.
Know Your Numbers. Always.
Profit Pioneers builds and maintains burn rate, runway, and cash flow dashboards for funded startups every single month.
Book Your FREE Financial AuditThis article is for informational purposes only and does not constitute legal, tax, or financial advice. Consult with a qualified professional for advice specific to your situation.