What a FIRE calculator should actually do
A good FIRE calculator answers three questions: 'when can I stop working?', 'what changes that date the most?', and 'how confident can I be in the answer?'
Most apps stop at the first question. Better tools let you change the inputs (savings rate, expected return, target spend) and watch the date move. The best add a confidence dimension — historical or Monte Carlo simulation — so you know whether your 12-year plan has a 95% chance or a 60% chance of holding up.
There's no single 'best' tool. The best one for you depends on whether you want it on your phone, whether you want it linked to your live net worth, and how much you care about probabilistic modeling vs. a clean deterministic answer.
1. WealthMap — best if you want it on your phone, linked to your real portfolio
WealthMap's FIRE calculator is the only one of these tools that lives inside a real net worth tracker on iOS. Your current portfolio value, savings rate, and target spend are pulled from your actual data — no separate spreadsheet, no double entry.
The What-If slider is the centerpiece. Drag your monthly savings up or down and watch your FIRE year shift in real time. It also flags CoastFIRE automatically — the point where you can stop adding money and still hit your number on schedule.
What it doesn't do: full Monte Carlo simulation. WealthMap uses a deterministic projection with adjustable real-return assumptions. If you need probabilistic confidence intervals, ProjectionLab or cFIREsim are better.
Pricing: €69.99 lifetime (or €5.99/month, €34.99/year). iOS 18.6+.
2. ProjectionLab — best for desktop power users
ProjectionLab is the most powerful scenario-modeling tool in the FIRE space. Multiple income streams, tax modeling, account-type segregation (taxable / tax-deferred / Roth), Social Security, pensions, custom milestone events — it handles all of it.
It runs in the browser, with optional account import. The learning curve is real, but for someone planning a complex retirement (multiple properties, business income, mid-career sabbaticals), nothing else comes close.
Price: $9/month or $108/year.
3. cFIREsim — best free Monte Carlo simulator
cFIREsim is the open-source workhorse of the FIRE community. It runs Monte Carlo simulations against historical US market data and tells you the percentage of retirement scenarios that succeed at your spending plan.
The UI looks like a tax form, but the math is solid and the tool is free. If you want probabilistic confidence ('this plan worked in 94% of historical 30-year periods'), cFIREsim is the standard.
4. Networthify — best for the one-line answer
Networthify is a single-page calculator: enter your income, savings rate, and target multiple — get a years-to-retire number. That's it.
It's based on the classic Mr. Money Mustache 'shockingly simple math' post. Useful as a sanity check or for quick comparisons, but not for planning.
5. FIRECalc — best for historical backtesting
FIRECalc takes your portfolio and spending plan, then asks: 'how often would this have worked if you'd retired in any year of US market history since 1871?' The answer is a success rate and a fan chart of all the historical paths.
It's free, the methodology is well-documented, and it's the right tool if you want to understand sequence-of-returns risk in a visceral way.
When to choose which
Choose WealthMap if: you want the calculator on your phone, linked to your actual portfolio, with a real-time What-If slider and CoastFIRE detection.
Choose ProjectionLab if: you want elaborate scenario modeling and you're happy doing it at a desk.
Choose cFIREsim if: you want free Monte Carlo confidence intervals and don't mind a dated UI.
Use a combination if you're serious — WealthMap for daily check-ins and CoastFIRE awareness, plus an annual run through cFIREsim or ProjectionLab to pressure-test the plan.