Last updated: 2026-06-23

Understanding cash runway

Cash runway is the number of months a business can keep operating before it runs out of money. It is the most direct measure of how much time the current bank balance buys, given the rate at which cash is leaving. For a startup that is not yet profitable, runway sets a hard deadline: the point by which the company must reach break-even or raise more capital. Watching it closely turns an abstract worry about money into a concrete countdown.

The runway formula

Runway divides the cash available by the monthly net burn:

Cash on hand is the total of cash and equivalents currently available, including any recent funding. Net burn is cash out minus cash in each month — the genuine monthly decline in the balance once revenue is counted against spending. The result is the number of months the balance lasts if burn holds steady.

Net burn versus gross burn

The denominator matters. Gross burn is everything spent in a month, ignoring income. Net burn subtracts revenue from that, so it captures the real drain on the bank account. Runway is normally built on net burn, because revenue genuinely stretches how long the cash lasts.

A company spending $120,000 a month while bringing in $40,000 has a gross burn of $120,000 but a net burn of $80,000. Using gross burn would understate its runway by a third.

Worked example

A startup holds $1,000,000 after a seed round and burns $80,000 net per month.

The company has about twelve and a half months before the balance reaches zero, assuming burn stays flat. If hiring pushes net burn to $100,000, runway shortens to ten months; if revenue growth trims burn to $60,000, it extends to almost seventeen. Small changes in monthly burn move the deadline substantially.

How much runway is enough

A widely used guideline is to keep at least twelve to eighteen months of runway and to start raising the next round once six to nine months remain, because closing a round often takes several months of its own. Dropping below six months is generally considered tight, since it leaves little margin if a raise slips or revenue disappoints. The right buffer depends on how fast the business can cut burn and how predictable its revenue is, so these figures are starting points rather than fixed rules.

Three broad bands are common in practice:

A moving number, not a fixed one

Runway is a snapshot built on the assumption that burn stays constant, which it rarely does. Hiring, revenue growth, and cost cuts all shift it, so the figure is re-estimated whenever those inputs change. Treating runway as a live metric — recalculated each month against the latest cash balance and burn — keeps the countdown honest and gives the most warning before decisions about raising or cutting become urgent. To examine the spending side in more detail, pair this with the Burn Rate Calculator for gross and net burn.