Runway: the survival metric
Runway is the number of months your business can operate before running out of cash. For venture-backed startups, it is the oxygen gauge — when it drops below 6 months, everyone panics. For bootstrapped businesses, it is the reserve buffer — the number of months you can survive a revenue drop before needing to act. Either way, every founder should know this number within $1,000 at any given time.
The basic formula is Runway = Cash / Monthly Burn, where burn is monthly expenses minus monthly revenue. If expenses are $40,000 and revenue is $15,000, monthly burn is $25,000. On $200,000 cash, runway is 8 months flat. If revenue grows 8% per month, it may stretch to 11–14 months. The calculator above models both — flat and growth-adjusted — so you see the range.
Gross burn vs net burn
Gross burn is total monthly expenses. Net burn is expenses minus revenue — the cash actually leaving the bank account. Investors and boards usually discuss net burn; operators should track both. Cutting expenses lowers gross burn; growing revenue lowers net burn without cutting. Both are levers, and in a cash crunch you pull both at the same time.
The 18-month rule for venture-backed startups
Standard advice for venture-backed companies is to maintain at least 18 months of runway at all times. Fundraising takes 3–6 months if everything goes well. If you start fundraising at 18 months and it takes 6, you close the round at 12 months — still plenty of buffer. Starting fundraising at 12 months of runway is risky; 9 months is dangerous; 6 months and below, your negotiating leverage evaporates and you accept bad terms or fail.
The 6-month rule for bootstrapped businesses
Bootstrapped businesses without venture lifeline usually target 3–6 months of operating expenses as cash reserve. This is different from runway — bootstrapped businesses are typically cash flow positive, so the "runway" is really "how long can we survive if revenue disappears." A service business with $40K monthly expenses should target $120K–$240K reserve. A product business might target 6–9 months given longer sales cycles.
Why the growth-adjusted runway matters
Simple runway assumes revenue stays flat. Growth-adjusted runway assumes revenue continues to grow at your current rate, which lowers burn each month. The calculator shows the difference. A startup at $15K MRR growing 10% per month on $200K cash has roughly 8 months of flat runway and 14+ months of growth-adjusted runway. The gap between the two numbers is your growth buffer. Aggressive growth assumptions in the model can be dangerous; conservative flat assumptions are safer but may underprice your real survival odds.
Extending runway when you need to
If the calculator shows unacceptably short runway, there are five levers to pull, usually in this order.
- Cut non-critical expenses. Software subscriptions, agencies, contractors, travel. Aim for 15–25% expense reduction in week one.
- Pause hiring. Hiring freezes are the single biggest operational cost lever. Defer any open reqs until runway is back above 12 months.
- Accelerate collections. Call every receivable. Offer small discounts for upfront pay. Convert monthly plans to annual plans with a 10% discount.
- Layoffs. The last resort. Cut deep once; cutting twice is psychological devastation for the team.
- Raise capital. Debt, equity, or bridge from existing investors. Start months before you absolutely need it.
Burn multiple — the VC-era efficiency metric
Burn multiple is Net Burn / Net New ARR. It measures how much you spend to add a dollar of ARR. Benchmarks (post-2022 sanity era):
- < 1× — amazing efficiency. Rarely seen.
- 1–1.5× — very efficient.
- 1.5–2× — healthy.
- 2–3× — concerning but workable.
- > 3× — you are burning too much for the growth you are getting. Efficiency, not more spend, is the fix.
Bootstrapped businesses rarely think about burn multiple, but the mental frame is useful: every dollar of burn should be producing a predictable return in revenue growth. If it is not, stop spending it.
When to stop burning
Some founders burn indefinitely expecting the next round to bail them out. That strategy worked 2012–2021 when cheap capital was abundant. Post-2022, the bar is higher. If you cannot demonstrate either clear path to breakeven in 24 months or genuinely exceptional growth (triple-digit YoY), investors are unlikely to fund the next round. Plan for profitability as the default outcome, with fundraising as the upside.
Runway and personal runway
Founders of bootstrapped businesses should track personal runway separately from business runway. How many months could you personally survive without taking a paycheck from the business? If the answer is less than 3 months, a small business dip becomes a personal crisis. Keep at least 6 months of personal expenses liquid outside the business, always.
Pair with other metrics
Runway is a lagging indicator — by the time it is short, you are in trouble. Pair it with the cash flow projector for month-by-month visibility, the MRR calculator for revenue trajectory, and the break-even calculator to see how many units get you to profitability. Checking runway monthly takes five minutes and is the single most-important financial metric for any venture-stage or early-stage business.