How to Calculate Startup Runway (Formula + Free Calculator)

What is runway?

Runway is the number of months a startup can keep operating with the cash it has today. It is calculated by dividing cash in the bank by monthly net burn. A startup with $300K in cash burning a net $30K per month has 10 months of runway. When runway runs out, the company must survive on revenue, raise funding, or shut down.

The term comes from aviation: the plane has to take off before the runway ends. For a startup, taking off means becoming self-sustaining on revenue or closing the next funding round. That's why runway is not just an accounting number — it is a measure of your freedom to make decisions.

How do you calculate runway?

The formula is simple: Runway (months) = Cash on Hand ÷ Monthly Net Burn. Net burn is your total monthly spend minus monthly revenue. At the earliest stage, with no revenue, net burn equals gross spend; as revenue grows, the two diverge and runway extends.

The critical mistake is computing it once with today's burn and assuming it stays flat. New hires, annual tool renewals, and collection delays move burn from month to month. Runway should be a number you update every month, not a one-time calculation.

A worked example

Say you have $240K in the bank. Monthly spend is $45K, monthly revenue is $15K; net burn comes to $30K. Runway = 240,000 ÷ 30,000 = 8 months. If the same company hires two engineers and pushes burn to $42K, one decision cuts runway from 8 months to 5.7.

Conversely, if revenue grows from $15K to $25K, net burn drops to $20K and runway stretches to 12 months. These are the two levers for extending runway: cutting spend or growing revenue. A good founder reads both on the same sheet.

How many months of runway is healthy?

The common rule is to start each period between rounds with 18–24 months of runway, because preparing and closing the next round can take 6–9 months. When runway drops below 12 months, you switch into fundraising mode; below 6 months, you run the defensive plan — cost cuts, a bridge round, or a push to profitability.

These thresholds are reflexes, not laws. They shift with sector, growth rate, and market conditions. The constant is this: a founder trying to manage runway with three months left has already lost their negotiating power at the table.

Ways to extend your runway

The first lever is spend: slowing the hiring plan, cutting unused tools, shrinking office and operations costs. The second lever is revenue: revisiting pricing, closing annual prepaid deals, shortening collection cycles.

The third and riskiest lever is new capital. Funding extends runway, but in a company that doesn't know why it burns money, it only makes the mistake more expensive. First be clear about what your burn is buying — learning, growth, or just time.

Scenario planning: base, bear, and bull runway

A single runway number hides the uncertainty that actually matters, so plan three versions. Base case: current burn and the revenue plan you genuinely believe. Bear case: the two biggest deals slip, one churn event lands, and a planned hire you can't avoid starts early — recompute runway with that burn. Bull case: revenue beats plan and you deliberately reinvest part of the surplus.

The bear case is the one that earns its keep: it tells you the real date by which fundraising must start, and it is almost always 2–4 months earlier than the base case suggests. Write all three numbers down monthly. When the actuals start tracking the bear case for two consecutive months, you switch plans — that trigger, agreed in advance, is what keeps the decision unemotional.

Default alive vs. default dead

Paul Graham's question compresses runway strategy into one test: with current growth and current burn, does the company reach profitability before the cash runs out? If yes, you are default alive — fundraising becomes a choice, taken for speed, not survival. If no, you are default dead, and the plan is a countdown that only a successful raise interrupts.

The value of the question is that it forces honesty about trajectory, not just balance. A company with 14 months of runway and flat growth is in worse shape than one with 9 months and compounding revenue. Knowing which side of the line you're on changes everything downstream: hiring pace, pricing courage, and how early you start round conversations.

A monthly runway routine that takes 15 minutes

First: read the actual bank balances — every account — and compute the three-month average net burn. Second: recompute runway with that number, not the budget's. Third: update the base and bear scenarios with what changed this month — a signed deal, a slipped deal, a new hire's start date. Fourth: check the thresholds — under 12 months means fundraising mode, under 6 means the defensive plan.

Fifth: write one sentence about what this month's burn bought — a shipped feature, a learning, a growth experiment. If the sentence is hard to write, that's the finding. The routine's power is not precision; it's that runway decisions get made on schedule, months before the bank account would force them.

Experiencing runway in a simulation

In Founder Runway, every decision hits the Cash and Runway metrics: a hire raises burn, an enterprise deal arrives with a collection delay, a funding round grows cash while touching the cap table. The gap between reading the runway formula in a spreadsheet and living its effect three turns later shows up exactly here.

Decisions you can't trial-and-error with real money — an aggressive hiring plan, an early sales team, a bridge round — you can safely test in the simulation.

Conclusion

Runway is as simple as cash divided by net burn; its real value appears when it becomes decision discipline. Update it monthly, price the runway cost of every major decision in advance, and treat the 12-month threshold as your alarm line. If you want the math done for you, the free runway calculator on this site takes your cash, spend, and revenue and returns your months of runway instantly.