Why cash runway is the #1 metric for startups
For early-stage companies, profitability is a future goal — cash runway is the present reality. Runway is the number of months you can keep operating at your current burn rate before running out of cash. The classic startup failure isn't building something nobody wants — it's running out of cash before proving you've built something people want.
The 18-month rule
Most venture capitalists want portfolio companies to maintain at least 18 months of runway at all times. This gives 12 months to make progress and 6 months to raise the next round if needed. Below 12 months, founders get distracted fundraising instead of building. Below 6 months, you're in survival mode — and investors know it.
Three ways to extend runway
- Cut burn: The fastest lever. Layoffs, rent reduction, marketing cuts. Painful but immediate.
- Grow revenue: The healthy lever. Each new dollar of recurring revenue extends runway permanently.
- Raise capital: The dilutive lever. Selling equity adds cash but reduces founder ownership.
Gross burn vs net burn
Gross burn = total monthly expenses. Net burn = expenses − revenue. A company with $100K monthly expenses and $60K monthly revenue has a gross burn of $100K but a net burn of only $40K. Investors care about net burn — it's the rate at which cash is actually disappearing.
Rule of 40: a healthy SaaS company's revenue growth rate (%) plus profit margin (%) should equal at least 40. 30% growth + 10% margin = 40 (good). 50% growth + -10% margin = 40 (acceptable). Below 40, the business isn't creating enough value to justify its cost of capital.
Frequently asked questions
What is cash runway?
The number of months a business can operate at its current burn rate before running out of cash. The #1 metric for startups. Below 12 months = concerning. Below 6 months = survival mode. Above 18 months = healthy.
What is the difference between gross burn and net burn?
Gross burn = total monthly expenses. Net burn = expenses − revenue. A company with $100K monthly expenses and $60K monthly revenue has $100K gross burn but only $40K net burn. Investors care about net burn — it's the rate cash actually disappears.
How much runway should a startup have?
Most VCs want 18+ months of runway at all times. This gives 12 months to make progress and 6 months to raise the next round. Below 12 months, founders get distracted fundraising. Below 6 months, you're in survival mode.
How do I extend my runway?
Three options: (1) cut burn (layoffs, rent reduction, marketing cuts — fastest), (2) grow revenue (healthiest — each new dollar extends runway permanently), (3) raise capital (dilutive but extends runway). Most founders use a combination.
What is the Rule of 40?
A SaaS benchmark: revenue growth rate (%) + profit margin (%) should equal at least 40. 30% growth + 10% margin = 40 (good). 50% growth + -10% margin = 40 (acceptable). Below 40 = underperforming vs cost of capital.
Should I raise money or bootstrap?
Depends on goals. Bootstrap if: market is small, you can reach profitability on founder savings, you value control. Raise VC if: market is huge, you need to move fast, you can scale revenue 5-10× with capital. Both are valid — choose based on ambition and risk tolerance.
What is a 'down round'?
Raising money at a lower valuation than your previous round. Triggers 'anti-dilution' provisions that hurt founders and early investors. Avoid by raising less at a flat valuation, or extending runway through cost cuts until you can raise at a higher valuation.
Glossary of key terms
- Burn Rate
- Rate at which a company spends cash. Gross burn = total expenses; net burn = expenses − revenue.
- Runway
- Months of operation possible at current burn rate before cash runs out. Cash balance ÷ monthly burn.
- Series A/B/C
- Successive funding rounds. Series A: $5-15M. Series B: $20-50M. Series C+: $50M+.
- Rule of 40
- SaaS benchmark: revenue growth rate + profit margin should equal at least 40.
- Term Sheet
- Non-binding agreement outlining key terms of an investment. Negotiated before final legal docs.
Common mistakes to avoid
- Confusing gross burn with net burn — net burn is what actually depletes cash
- Not calculating runway until fundraising — by then it may be too late to extend
- Cutting growth investments to extend runway — sometimes kills the business more slowly
- Raising too much money at too high a valuation — sets up down round risk
- Not modeling revenue growth in runway calculations — overly pessimistic projections lead to bad decisions
Pro tips
- Track runway monthly — it's the #1 startup survival metric.
- Maintain 18+ months of runway at all times — gives buffer to raise next round.
- Model multiple scenarios — base case, downside, worst case. Plan for the worst, hope for the best.
- Cut costs proactively when runway drops below 12 months — don't wait until crisis.
- Consider revenue-based financing or venture debt before equity raises — less dilutive.
Results are estimates for educational purposes only and not financial advice. Consult a licensed professional for advice specific to your situation.