The Runway Calculator converts your cash position into the number founders actually plan around: how many months until the money runs out. Enter your cash balance and monthly expenses, optionally monthly revenue and a monthly expense growth rate, and it returns flat runway, growth-adjusted runway, your projected balance in six months, and the dates the cash hits zero and fundraising should begin.
How It Works
Net burn is monthly expenses minus monthly revenue. Flat runway divides cash by net burn. If you enter an expense growth rate, a month-by-month simulation replaces the simple division: each month the burn (that month's grown expenses minus revenue) is deducted and expenses compound upward, which always shortens the runway. A business whose revenue covers expenses is reported as profitable with no runway limit, provided expenses are not growing into the revenue line.
Parameters
| Input | Required | Meaning | |---|---|---| | Cash balance | Yes | Cash available today | | Monthly expenses | Yes | Total monthly cash out | | Monthly revenue | No | Monthly cash collected (not just booked) | | Expense growth rate | No | Monthly % growth in expenses, for the simulation |
Worked example
A startup holds 120,000 a month, and collects 100,000. Flat runway is exactly 9.0 months. Add 3% monthly expense growth and the simulation runs out in 8 months: growth consumes the ninth month because the burn in the final months is far above today's $100,000. The calculator also projects the six-month balance and derives two dates from the runway: when cash reaches zero, and a start-raising-by date set ahead of it, because a fundraise closed in the month the money ends is a fundraise that fails.
Runway is a planning date, not a death date
The number's real use is sequencing decisions. With eighteen months, the plan is milestones. With nine, the plan is milestones plus a raise starting by month four. With five, the plan is a bridge, a cut list, or a revenue emergency, chosen now while all three still exist. Teams get into trouble by re-reading the same runway figure for months while burn quietly grows; the growth simulation in this calculator exists precisely to show how a "nine-month" company is an eight-month company on its current hiring plan.
Extending runway: the honest levers
Reduce net burn (cuts, renegotiations, slower hiring), increase collections (upfront annual billing, tighter terms, dunning on failed payments), or add cash (raise, venture debt, grants). Each lever has a runway exchange rate you can compute here before acting: at a 10,000 monthly cost saving buys about one extra month; a one-time $100,000 cash injection buys exactly one month; growing expenses 3% monthly takes roughly a month away. Levers that change the monthly burn beat one-time injections over any horizon longer than a quarter.
Limitations
The simulation grows expenses smoothly and holds revenue flat; real revenue moves too, in both directions, and lumpy items (annual renewals, tax payments, a churned whale) break the smooth curve. Zero-cash dates are projections from today's inputs, not predictions. Recalculate monthly from bank balances, and treat any month where actual burn beats the model as a signal to re-plan, not to average it away.
A simple operating rhythm for runway
Recalculate runway monthly from the bank balance, not from the accounting system, and write the number where the whole leadership team sees it. Pair it with two commitments: the trigger points agreed in advance ("at nine months we start the raise; at six we enact the cut list") and a rolling thirteen-week cash forecast for the near term, where payroll dates, quarterly tax, and annual renewals actually live. Runway tells you the size of the cliff; the weekly forecast tells you about the potholes on the way there, and companies are killed by both.
Hiring is a runway decision
Every hire is a recurring burn increase with a compounding growth tail in this model. A single $12,000-a-month fully loaded hire at the worked example's position cuts flat runway from 9.0 months to about 8.0 months on the spot (900,000 / 112,000), before any growth assumption. That does not make the hire wrong; it makes the trade explicit. Founders who quote runway to justify a hiring plan should quote the runway after the plan, which is the only version the bank account will ever see.
Frequently Asked Questions
What runway should I have before fundraising?
Start the raise with at least six months of runway remaining after the expected closing timeline, which in practice means beginning around nine to twelve months of runway so the money lands with a buffer. Running the process at three months of runway negotiates against you.
Does the calculator count revenue I have invoiced but not collected?
Enter collected cash. Invoiced-but-unpaid revenue does not pay salaries, and counting it is the most common way runway gets overstated in young companies.
What if my revenue exceeds expenses?
The calculator reports the business as profitable with no runway limit on current figures. Add an expense growth rate and it will show whether planned growth spends you back into a finite runway.