What Is FIRE?
FIRE stands for Financial Independence, Retire Early. It's both a philosophy and a mathematical framework built on one central idea: by saving and investing a much higher percentage of your income than conventional wisdom suggests, you can achieve financial independence — the state where your investments generate enough passive income to cover your living expenses permanently — decades before the conventional retirement age of 65.
"Retire Early" doesn't necessarily mean stopping all activity at 35. For most FIRE practitioners, it means reaching the point where work is optional — a choice made because of interest or purpose, not financial necessity.
The movement traces to Vicki Robin and Joe Dominguez's 1992 book Your Money or Your Life and gained mass momentum through personal finance blogs and communities in the 2010s. Today, millions of people across income levels and countries are pursuing some version of FIRE — from coastfire to aggressive full FIRE to Fat FIRE.
The Fire Formula — The Mathematics of FIRE
Every FIRE calculation starts with the fire formula (also called the fire equation):
At the standard 4% SWR: FIRE Number = Annual Spending × 25
Examples:
$40,000/year spending → $1,000,000 FIRE number
$55,000/year spending → $1,375,000 FIRE number
$80,000/year spending → $2,000,000 FIRE number
The 4% safe withdrawal rate comes from the Trinity Study (1998), which analysed historical US market data and found a portfolio of 50%+ equities could sustain a 4% annual withdrawal with ~95% historical success over 30-year periods.
To answer "what is my fire number?": multiply your expected annual retirement spending by 25. Then, for your coast fire number — the smaller, earlier milestone you can target first — use our free coast fire retirement calculator.
The Main FIRE Variants
FIRE is a spectrum. Understanding the variants helps you choose the right path for your situation:
Coast FIRE (Coastfire)
Invest enough early that compound interest handles the rest. You keep working to cover current expenses but stop saving for retirement. The fastest milestone — use the coastfire calculator to find your number.
Lean FIRE
Full independence on a minimal budget — typically under $40,000/year. Smallest portfolio required; highest lifestyle discipline needed.
Regular FIRE
The standard path — 25× annual spending in a diversified portfolio, then retire fully at your chosen age.
Fat FIRE
Full independence at an above-average lifestyle — $80,000–$150,000+/year. Larger portfolio; more spending freedom.
Barista FIRE
Part-time work supplements a partially-funded portfolio. Earlier exit from full-time work; often accessed for employer healthcare benefits.
Flamingo FIRE
Save to half your full FIRE number, then work part-time while investments compound the rest — similar logic to coastfire but different threshold.
Why Savings Rate Matters More Than Income
The most counterintuitive FIRE insight: your savings rate — not your income — determines how fast you reach any FIRE milestone. A $70,000 earner saving 50% reaches coastfire faster than a $200,000 earner saving 10%.
| Savings Rate | Years to Full FIRE | Retirement Age (starting at 25) |
|---|---|---|
| 10% | ~43 years | ~68 — conventional |
| 25% | ~31 years | ~56 |
| 40% | ~22 years | ~47 |
| 50% | ~17 years | ~42 |
| 65% | ~10.5 years | ~36 |
The coastfire number changes this table dramatically. Because coast FIRE requires only a discounted fraction of the full FIRE portfolio, the intense saving period is much shorter — often 5–10 years for consistent investors in their mid-20s. Use the free coast fi calculator to find your personal coastfire number by age.
Coast FIRE as the First Milestone
For most people starting their FIRE journey, coastfire is the most actionable first target. Here's why:
- The coast fire number is typically 70–90% smaller than the full FIRE number
- It's achievable in 5–12 years for disciplined savers — versus 15–25 for full FIRE
- Once reached, career flexibility opens immediately — you can earn less, work less, or change fields entirely
- It provides meaningful financial security without the extreme discipline of maintaining 40–60% savings rates for decades