The math behind your shore line.

Coast FIRE is a free, no-sign-up calculator suite for figuring out when you can stop worrying about money. Seven calculators, one design system, zero dark patterns.

What this site does

Each calculator answers one specific question — when can I coast? what is my FIRE number? is 4% safe? — using transparent math you can inspect. Every assumption (7% nominal return, 3% inflation (about 3.9% real), and a 4% withdrawal rate) is documented on the calculator page itself and linked to a plain-English explainer in the Journal.

There is no account, no email capture, no "tip of the week" newsletter. You arrive, you run your numbers, you leave with a plan. That is the entire product.

What "Coast FIRE" means

Traditional FIRE asks you to save 25x your annual expenses, then quit working forever. Coast FIRE is a softer version: you save enough that compound growth alone carries your portfolio to your full FIRE number by your target retirement age. After that, every dollar you earn is optional.

For a 35-year-old with $100,000 invested at 7% nominal return (about 3.9% real after 3% inflation), that money grows to roughly $260,000 in today's dollars by age 60 — without adding another cent. Not a full FIRE number on its own, but proof that time does the heavy lifting. The math is not magic — it is compound interest, honestly applied.

How the calculators work

• Every calculation runs in your browser, in real time, as you drag the sliders.
• The math is a small TypeScript library of pure functions. The same code runs our tests, so what you see matches what we verify.
• Numbers use tabular figures so columns align. Currency uses your locale. Nothing rounds silently.
• The 4% rule, Trinity Study success rates, and the MMM savings rate table are all pulled from published research, not invented here.

What this site does not do

• No account, no email, no newsletter.
• V1.0 shows no ads and no paid promotional links. If affiliate recommendations are added in the future, they will be clearly labeled as such.
• No tracking beyond anonymous aggregate page views (analytics for event counts only).
• No financial advice. The numbers are inputs, not advice.

Who built this

Coast FIRE is an independent solo project, built because its creator got tired of "FIRE calculator" sites that buried the math behind popups, email walls, and promotional links. The visual style — warm coastal colors, frosted glass, no template-y cards or emoji — was built so the site feels like the morning you realize the math is on your side.

The fine print

Read the full disclaimer for the legal version, but the short version is: these calculators are educational tools, not financial advice. Past returns do not predict future ones. Talk to a fiduciary before making decisions with real money.

Last updated: September 2026