Runway calculator

“Default alive” is the single most important question about an early-stage business, and it comes from Paul Graham: if you keep spending and growing at your current rate, do you become profitable before the money in the bank runs out? If yes, you are default alive — you control your own fate. If no, you are default dead, and you are quietly relying on raising more money or a sudden change you have not planned. This calculator runs that test on your own numbers: it grows your revenue month by month and watches whether it overtakes your spending before your cash hits zero.

The distinction matters because default-dead founders often do not feel in danger — the bank balance is still positive, the charts point up and to the right. But a positive balance today says nothing about the trajectory. A company burning $40,000 a month with $200,000 in the bank has five months, not “plenty.” Knowing which side of the line you are on changes every decision: default-alive companies can afford to invest in growth; default-dead companies need to either cut burn or line up funding now, while there is still runway to negotiate from a position of strength.

A single runway figure — “eight months” — flattens a moving picture into one point. Two things move underneath it. The first is revenue: if you are growing, every month your income covers more of your costs, so your effective burn shrinks and your real runway is longer than a flat calculation suggests. That is why this tool lets you add a monthly growth rate and then shows the cash curve bending, not just sliding straight to zero. The second is lumpy costs — a tax bill, a big hire, an annual software renewal — which a smooth “burn rate” average completely hides. The one-off cost field exists so a single large payment next month shows up as the cliff it really is.

The other thing the headline number hides is how sensitive it is. Runway reacts hard to small changes in spending, because burn is the denominator. The insights under your result make that concrete: they show what cutting spending 15% would buy you in extra months, and — if revenue is growing but too slowly — exactly how many months short of break-even your cash leaves you. Those are the levers. Seeing them in months, against a real calendar date, is what turns “we should probably watch our spending” into “rent is due in March and we are out of cash in February.”

Three numbers describe the same situation from different angles. Burn rate is how much cash you lose in a month — your money out minus your money in. Runway is how long your current cash lasts at that burn: cash in the bank divided by monthly burn. The zero-cash date is that runway laid onto a calendar, the month you would hit empty if nothing changes. This calculator reports all three at once, because founders think in different units at different moments — an investor asks for months of runway, a cofounder asks “until when,” and you cut costs against the burn.

The subtle part is that burn is not constant when revenue grows. A naïve runway of cash ÷ (this month’s burn) assumes your income never improves, which understates a growing company and overstates a shrinking one. Simulating month by month — as this tool does — is the honest version: it recomputes each month’s revenue, subtracts each month’s costs, and finds the exact month the balance crosses zero, or confirms it never does because revenue caught up first.

There are only three levers, and the calculator lets you test each in seconds. Cut spending: because burn is the denominator, trimming it moves runway more than almost anything else — the result panel spells out what a 15% cut would add. Grow revenue faster: raise the growth rate and watch whether the cash curve bends up enough to cross into default-alive territory before zero. Or add cash: a raise, a loan, revenue pulled forward — anything that lifts the starting balance shifts the whole curve up and pushes the zero-cash date out.

The goal is not the longest possible runway for its own sake; it is reaching default alive with margin to spare. Once monthly revenue reliably covers monthly costs, runway stops being a countdown and becomes a choice about how fast to reinvest. Getting there is a growth problem — the specific customers, offer, and marketing that lift revenue past the line — and that is exactly the plan SoGood builds for your business.