Built for the FIRE community
ReachFire is a free FIRE calculator with geoarbitrage, Roth ladder planning, and AI insights. Every calculation runs in your browser. We never see your data.
Privacy Commitment
All calculations run 100% in your browser using JavaScript. Your financial data never leaves your device. There is no account to create, no database storing your numbers, and no tracking of your inputs.
The only exception is the optional AI Insights feature, which sends anonymized financial parameters (no personal identifiers) to Anthropic's Claude API for analysis. This requires explicit user action — clicking "Get AI Analysis." No other feature sends any data to any server.
ReachFire uses no advertising, no analytics pixels, and no third-party tracking scripts. We earn nothing from your data because we collect none of it.
Methodology
FIRE Number
The FIRE number is calculated as Annual Expenses ÷ Withdrawal Rate. The default 4% withdrawal rate comes from the Trinity Study (1998) by Cooley, Hubbard, and Walz, which found that a 4% withdrawal rate from a diversified portfolio historically sustained 30-year retirements with high probability. For longer retirements (40+ years), we recommend 3.5%.
Portfolio Projection
Projections use the standard future value formula with monthly compounding:FV = PV × (1 + r)ⁿ + PMT × ((1 + r)ⁿ - 1) / rWhere r is the monthly return rate (annual rate ÷ 12) and n is the number of months. Real (inflation-adjusted) returns use the Fisher equation: (1 + nominal) / (1 + inflation) - 1.
Monte Carlo Simulation
Monte Carlo simulations use a log-normal return distribution based on historical S&P 500 statistics. The standard deviation defaults to ~17% annually, derived from the Shiller dataset. Each simulation generates random annual returns using the Box-Muller transform for normally distributed random variables, then exponentiates them for log-normal returns. We run 1,000 simulations by default. Success rate = percentage of simulations where the portfolio survives to the end of the projection period.
Historical Backtesting
Historical backtesting uses actual annual returns from the Shiller dataset (1926–2024), which tracks S&P 500 total returns (price + dividends) and long-term US government bond returns. For each start year from 1926 to (current year - duration), we simulate the specified withdrawal strategy using actual historical returns. The success rate is the percentage of historical 30-year periods where the portfolio survived.
Healthcare Cost Projections
ACA (Affordable Care Act) premium estimates are based on the 2025 benchmark silver plan premiums by age band and the premium tax credit formula from KFF's Health Insurance Marketplace data. Subsidies follow the American Rescue Plan Act extension rules (capped at 8.5% of income for incomes above 400% FPL). Medicare cost estimates use 2025 Part B standard premiums ($174.70/month) with IRMAA surcharges from CMS data. Healthcare inflation is modeled at 5.5% annually (20-year historical average). These are estimates — actual costs vary significantly by state, plan, and health status.
Key Assumptions
- ·Returns are inflation-adjusted in real-dollar mode using the Fisher equation
- ·Monthly contributions are assumed to be invested at the end of each month
- ·Social Security income is not included in projections by default
- ·Tax efficiency of investments is not modeled (use the tax tools for tax analysis)
- ·Coast FIRE calculations assume contributions stop completely at the coast age
- ·Roth conversion ladder assumes the 5-year seasoning rule applies to each separate conversion
- ·Geoarbitrage adjustments are linear based on cost index ratios — lifestyle adjustments may vary
- ·Medical tourism savings estimates include $2,500 estimated travel costs
- ·Default asset allocation for historical backtesting: 60% stocks / 40% bonds
Data Sources
Important Disclaimer
ReachFire is not a financial adviser, investment adviser, broker-dealer, tax adviser, or legal professional of any kind. Nothing on this platform constitutes financial, investment, tax, accounting, or legal advice.
All projections, simulations, and estimates are hypothetical and for illustrative purposes only. They are based on mathematical models and historical data that may not reflect current conditions or your individual circumstances. Past market performance does not guarantee future results.
Tax calculations use simplified models based on 2025 IRS data. Social Security estimates use the SSA bend-point formula but do not use your actual earnings record. Healthcare cost estimates are approximations — actual premiums vary by state, plan, and health status. Always verify with official sources (IRS.gov, SSA.gov, HealthCare.gov, CMS.gov).
Before making any financial, retirement, tax, or investment decisions, consult a qualified professional — such as a Certified Financial Planner (CFP), Registered Investment Adviser (RIA), Certified Public Accountant (CPA), or attorney — who can evaluate your specific circumstances.
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