Evaluation guide
How to compare FIRE calculators
Start with the decision you need to make. A smooth projection, a Monte Carlo model and a historical-cycle test answer different questions.
Three common methods
| Method | Useful for | Main limitation | Available here |
|---|---|---|---|
| Fixed return | A clear baseline and sensitivity checks | Hides the order and variability of returns | Yes |
| Monte Carlo | Testing many randomized return paths under chosen assumptions | Results depend on the return model and inputs | Yes, simplified independent annual returns |
| Historical cycles | Seeing how a plan handled observed market and inflation sequences | Past US data is not a forecast or a complete global sample | Yes, overlapping US windows from 1928–2025 |
A practical checklist
- Can you see whether values are nominal or in today's money?
- Does the result distinguish reaching a target from sustaining spending through the full horizon?
- Can you include ongoing retirement income and dated income or expenses?
- Does it show an unreachable result instead of inventing a retirement date?
- Can you inspect the data period, assumptions and calculation limitations?
- Can you rerun the same plan under lower returns, higher spending and a lower withdrawal rate?
Verified scope of The FI Calculator
The current model provides fixed-return accumulation and drawdown, Coast FIRE, dated cash-flow events, Monte Carlo paths and historical US stock/Treasury/inflation windows. Its calculations run locally in your browser. It does not model taxes, fees, country pension rules or portfolio rebalancing.
We have not completed a current hands-on audit of named competing calculators, so this page does not rank them or claim feature differences. Apply the checklist to any tool you consider.
Use results as ranges
No calculator predicts markets. Compare several plausible assumptions, understand which inputs drive the answer, and revisit the plan as your spending, income and portfolio change. These tools provide educational estimates, not financial advice.