FIRE (Financial Independence, Retire Early) is a personal finance movement built around the idea that aggressive saving and investing can free you from mandatory work decades ahead of the conventional retirement age. It grew from the Boglehead and frugality communities of the 1990s–2000s, gained mainstream visibility through bloggers like Mr. Money Mustache, and has since spawned dozens of specialized variants for different income levels and lifestyle goals. The central insight that makes FIRE tractable — and that most people miss — is that your savings rate, not your income, determines how long you must work: a household saving 50% of income needs roughly 17 years to retire regardless of absolute income, while one saving 10% needs over 50 years.
What This Cheat Sheet Covers
This topic spans 15 focused tables and 114 indexed concepts, 108 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
A jump-to index of every table row in this cheat sheet.
An interactive map of every table and concept in this topic.
Table 1: Core FIRE Concepts and Definitions
Every FIRE journey begins with the same small set of foundational formulas and mental models. Understanding the 4% Rule, the 25x target, and the savings-rate math is the prerequisite for every other decision in the FIRE framework.
| Concept | Example | Description | |
|---|---|---|---|
Spend $40,000/yr → need $1,000,000 portfolio | • Withdraw 4% of your portfolio in year 1, then adjust for inflation each year • originally validated on 30-year horizons by Bengen (1994). | ||
Annual expenses $50,000 × 25 = FIRE number $1,250,000 | • The portfolio size that allows a 4% withdrawal rate • the direct mathematical inverse of the 4% Rule | ||
Annual expenses ÷ 0.04 = FIRE number | • Your personal portfolio target at which you can retire • recalculated whenever annual spending changes | ||
Save $40,000 on $100,000 income → 40% rate | • Percentage of income saved and invested • the single biggest lever on your retirement timeline | ||
Portfolio covers all living expenses without employment | • The point at which investment income can permanently replace a paycheck • "retire" is optional — many keep working by choice | ||
10% → 51 yrs; 25% → 32 yrs; 50% → 17 yrs; 70% → 8.5 yrs | Higher savings rates compress the timeline dramatically because you both accumulate faster and need less portfolio at retirement. | ||
Working years of saving and investing toward FIRE number | • The years of active saving and investing before reaching FI • ends when portfolio reaches the FIRE number | ||
Withdrawing from portfolio to fund retirement lifestyle | • The post-FIRE years of living off investments • requires a withdrawal strategy to avoid portfolio depletion | ||
Continuing to work after FI in a passion project | • Reaching FI without necessarily retiring early • work becomes a choice rather than a financial necessity | ||
45-year retirement → safer withdrawal is ~3.5% → 28x target | For early retirees with 40–50+ year time horizons, Bengen's own research shows the safe rate drops to 3.5%, implying a 28x–30x target. |