About FIRE: Retirement Calculator
Method & principles · Updated September 2026
A focused, private FIRE calculator that does the math openly and stays out of your way.
What this is
FIRE: Retirement Calculator is a single-purpose iPhone app. It finds your FIRE number, projects the year your investments are expected to reach it, and puts a live countdown to that date on your home screen. Finding your number and the countdown are free. It is not a budgeting app, an account aggregator, or a brokerage — just the calculation and the countdown, done carefully.
How the numbers are calculated
None of it is a black box. Your FIRE number is your annual retirement spending divided by your safe withdrawal rate — at the common 4% rule, that is 25× your yearly expenses. The projection compounds your current investments and yearly contributions forward at your expected return and finds the first year the balance meets your number.
Returns are treated as real (after-inflation) by default, using the exact Fisher relation, so a figure decades out still means something in today's dollars. The 4% rule itself comes from the Trinity study and William Bengen's research on historical safe withdrawal rates — a well-tested benchmark, not a promise. The calculator on this website uses the same formulas as the app, so the two always agree. If a result ever surprises you, the app shows the formula worked through with your own figures.
The principles behind it
- Private by design. No account, no ads, no analytics, no third-party tracking. What you enter stays on your device, or syncs only through your own private iCloud — which the developer cannot read. The App Store privacy label is “Data Not Collected.” (See the privacy policy.)
- No subscription. The core — your FIRE number and the countdown — is free. Pro is an optional one-time purchase, never a recurring charge, and future features are included.
- No dark patterns. You see your FIRE number before any paywall. The free tier is meant to be genuinely useful on its own.
Educational, not advice
FIRE: Retirement Calculator is an educational planning tool. Its projections are deterministic illustrations based on the assumptions you enter — they are not guarantees, and not personalized financial, investment, or tax advice. For decisions about your own circumstances, speak with a qualified professional.
Who builds it
FIRE: Retirement Calculator is built by Kevin Lan, an independent app developer. It is a small, self-funded project — no investors, no data business, no advertising — which is exactly what makes the privacy and no-subscription choices above possible. Questions and feedback are welcome through the support page.