Strip away the acronyms and FIRE (Financial Independence, Retire Early) is two questions: how big a pot makes work optional, and when you reach it. The common shorthand for the first is roughly twenty-five times your annual spending — the point where a modest withdrawal each year can, historically, keep pace without draining the pot. It's a starting figure rather than a promise, but it turns a vague ambition into something you can aim at.
This calculator handles both halves. Put in your age, savings and what you invest each month, set a return and inflation, and it projects the balance forward to show when financial independence lands and whether it holds afterwards, all in today's money. If you're weighing a specific flavour — coast, lean, fat or barista FIRE — there are dedicated pages for those; this one is the general number-and-date view. The projection is free; the market survival test is a paid extra. Just try it and see what your FIRE date looks like on paper.