Runway Calculator

Runway (months) = Cash balance ÷ Net monthly burn. Net burn = monthly expenses − monthly revenue. Zero-cash date = today + runway. Growth-adjusted: project cash month by month as revenue and expenses grow; default-alive if revenue overtakes expenses before cash hits zero.

The simple runway — and why it’s not enough

Runway is cash divided by net burn: a company with 2.4 million in the bank burning 120,000 a month net has 20 months of runway, hitting zero around 20 months from today. That flat calculation is the right starting point and the number to know cold. But it bakes in an assumption that’s almost never true — that burn stays constant. In reality expenses creep up as you hire and revenue (hopefully) climbs, so the real cash curve bends. A growing company’s runway is usually longer than the flat figure suggests, because net burn shrinks as revenue catches up; a company hiring ahead of revenue can find its runway shorter. That’s why the projection matters as much as the headline.

Worked example — 2,400,000 cash, 300,000 expenses, 180,000 revenue: Net burn = 300,000 − 180,000 = 120,000/month. Flat runway = 2,400,000 ÷ 120,000 = 20 months → zero-cash date ≈ 20 months out. With revenue growing 10%/month and expenses 3%, the projection extends further — and may reach profitability first.

Default-alive or default-dead

Paul Graham’s framing cuts to the heart of it: a startup is default-alive if, on its current growth and spending trajectory, it reaches profitability before the money runs out — and default-dead if it doesn’t. The distinction is profound because it changes everything about how you should act. A default-alive company controls its own destiny and can raise from a position of strength (or not at all); a default-dead one must either raise or cut, and the longer it waits the worse its options. This calculator answers the question directly by projecting revenue and expenses forward month by month: if the revenue line crosses the expense line — net burn turns positive — before cash hits zero, you’re default-alive, and it tells you which month. The default-alive chart plots exactly that crossing.

Scenarios, raising, and the date that matters

Runway is a lever, not just a readout. The biggest lever is spending: the calculator models a lean scenario (cutting spend extends runway) and an aggressive scenario (hiring faster shortens it) alongside the current plan, so you can see the three zero-cash dates side by side — the scenario fan. The other lever is cash. Reverse mode works backwards from a target runway — say the 18 months investors like to see between rounds — and tells you how much you’d need to raise to get there. And entering an incoming round shows how the date moves out. Whatever the inputs, the number that concentrates the mind is the zero-cash date: a specific calendar day, not an abstract month count, and the deadline every other plan has to beat. Educational tool only, not investment advice.