The arithmetic is simple — cash divided by monthly burn — but the number is only as fresh as the update it came from. A founder who reported twelve months of runway in March has, by September, about six left if nothing changed. That gap is why Signed tracks implied runway: the months reported, less the months that have passed since, so the figure on a company's page keeps draining between updates instead of freezing at whatever the last email said. When it reaches zero, one of three things happened — the company raised, cut burn, or is in trouble — and all three are worth a note to the founder.
Runway also tells you when the next round is coming. Most founders start raising with six to nine months left, because a seed or Series A takes three to six months to close and nobody wants to negotiate from a position of weakness. So a company showing eight months of runway is a company about to ask you for a pro rata check, and one showing three is a company that either has a term sheet you haven't heard about or a bridge round on the way. Read runway alongside monthly burn and ARR: burn rising while runway shrinks is fine if revenue is growing to meet it, and alarming if it isn't.