What is the best FIRE calculator? The one that tells you your FI date and how you got it

Everyone asks, nobody agrees

"What is the best FIRE calculator" shows up on message boards constantly, and the answers are a pile of personal favorites. The truth: most of them solve the same equation, and the differences are in how honest the defaults are and whether they work in real terms.

What FIRE math actually needs

You want three things. Your FIRE number, which is annual spending divided by your withdrawal rate, usually 25 times spending at 4%. The years it takes you to get there, which compounds your current stash and monthly contributions. And the return number used in that compounding, which should be a real return, meaning after inflation, or the whole projection is cooked.

Where calculators lie to you

A nominal 7% return with 3% inflation is about 3.9% real. Running the projection at 7% instead of 3.9% does not just inflate the answer, it changes the timeline by a decade or more. A FIRE calculator that does not let you adjust inflation, or quietly ignores it, is a motivational poster with a number on it.

What a good one gives you

The FIRE calculator here works in real returns, shows the FI age and the year-by-year path, and credits your monthly contributions properly. No signup, nothing sent anywhere. It also respects the 4% rule's main catch, which our 4% rule breakdown covers: the 30 year horizon assumption.

My honest pick

Best FIRE calculator is the one you will actually re-run, because your spending and savings change every year. Re-running a good one yearly, and watching the FI date move toward you, beats picking the fanciest one once and never looking at it again. Use this one, revisit it in January, and you will be doing better than half the people arguing about it online.