Startup Runway Calculator

Why static runway math bankrupts growing (and shrinking) companies

Dividing cash by this month’s net burn assumes every future month looks like today. Founders then hire, buy gear, or miss a sales ramp and discover insolvency in a spreadsheet they trusted. The correct model is a cash walk: start with reserves after one-time outlays, apply this month’s revenue and expenses, grow (or shrink) revenue, and stop when cash hits zero, or when the company is profitable and burn is defined as $0.

Start cash = reserves − one-time capex
Revenue(1) = current operating revenue
Revenue(t) = Revenue(t−1) × (1 + growth / 100)
Net flow(t) = Revenue(t) − expenses
If flow ≥ 0 → burn = $0, infinite runway
Else cash(t) = cash(t−1) + flow(t) until cash ≤ 0 (max 120 months)

Defaults: $250,000 cash, $15,000 revenue, 5% monthly growth, $35,000 expenses, $0 capex. Month-1 net burn is $20,000. Revenue reaches $35,000 in month 19, and the remaining cash is still positive, so the badge reads Profitable / Infinite Runway. Set growth to 0% and the same cash lasts 12.5 months, a yellow caution pill and a zero-cash date about 12-13 months from today.

Reading the status pill, zero-cash date, and break-even month

Green is 18 months or more, or infinite. Yellow is 6 through 17.9 months. Red is under 6, including a zero-cash starting balance. The pill is text, not color alone. Net monthly burn is always month 1 (expenses minus current revenue, floored at $0) so you can compare the starting hole even when later months improve.

Zero-cash date is the calendar month when the walk hits zero, formatted like “October 2027”. It is blank when the company becomes cash-flow positive first, or when the 120-month cap is hit with cash left. Months to break-even is the first month whose grown revenue covers expenses, even if you would have run out of cash earlier. That tells you how fast sales must grow if you raise. “Never” means growth is too low (or negative) to catch the cost base inside 10 years.

Hiring, capex, and negative growth

This engine holds operating expenses constant. If you plan to hire, raise the monthly expense field to the fully loaded future run-rate, or treat the first payroll burst as a one-time outlay plus a higher ongoing expense. Understating future payroll is the usual way a 14-month runway becomes four.

One-time capital outlays come off the top. A $250,000 raise that is immediately spent on a $250,000 build is 0 months of runway, and the page says so with a critical alert. Negative growth is not a bug: a −10% monthly revenue decline on the defaults depletes cash in about 9.9 months because each month’s hole is larger than the last. That is the accelerating-burn case static calculators miss.

Projection stops at 120 months. If you still have cash, the KPI shows 120+ Months. Pair this with the Break-Even Calculator when you think in units rather than MRR, and with the SaaS LTV Calculator if the growth rate itself depends on paying more than a customer is worth.

Copy exports every input plus net burn, runway, status, zero-cash date, and break-even month. Paste it into a board update. Recalculate after every hire or pricing change; a model you do not reopen is how 18 months quietly becomes six. This is a planning walk with constant expenses, not a full three-statement forecast. It will not model delayed receivables, VAT, or a credit line. It will stop you from treating last month’s burn as a law of physics.

Frequently Asked Questions (FAQ)