Lean FIRE vs Fat FIRE Calculator: Which Number Is Right for You?

Lean FIRE needs $750,000. Fat FIRE needs $3 million or more. The difference is not ambition. It is your definition of a good day.

The FIRE movement has fractured into sub-strategies because $1.5 million retirement looks very different from $3 million retirement, and very different from $750,000 retirement. Here is the math behind each version.

The Four FIRE Types

Lean FIRE: Retiring on bare-bones spending, typically $30,000-$40,000 per year. Achievable with $750,000 to $1,000,000. Requires frugal lifestyle, usually with geographic flexibility (lower cost of living areas or geo-arbitrage).

Regular FIRE: The $40,000-$80,000/year range. Requires $1,000,000 to $2,000,000. Moderate lifestyle, some travel, no major luxury. The most commonly discussed version.

Fat FIRE: $100,000+ per year in retirement. Requires $2,500,000 to $4,000,000+. Full lifestyle maintenance, travel, dining, and giving without compromise.

Chubby FIRE: The middle ground between Regular and Fat FIRE. $80,000-$120,000/year, $2,000,000-$3,000,000 target. Comfortable but not lavish.

The Numbers Side by Side

| FIRE Type | Annual Spend | FIRE Number (4%) | FIRE Number (3.5%) | |-----------|-------------|-----------------|-------------------| | Lean FIRE | $30,000 | $750,000 | $857,000 | | Lean FIRE | $40,000 | $1,000,000 | $1,143,000 | | Regular FIRE | $60,000 | $1,500,000 | $1,714,000 | | Regular FIRE | $75,000 | $1,875,000 | $2,143,000 | | Chubby FIRE | $90,000 | $2,250,000 | $2,571,000 | | Fat FIRE | $120,000 | $3,000,000 | $3,429,000 | | Fat FIRE | $150,000 | $3,750,000 | $4,286,000 |

Using 3.5% withdrawal is more conservative and appropriate for retirements lasting 40+ years.

What Lean FIRE Actually Looks Like

$30,000 per year is $2,500 per month. Before healthcare. In a medium cost-of-living city, that covers:

• Rent or mortgage: $900
• Groceries: $400
• Transportation: $250
• Utilities and phone: $200
• Healthcare (ACA subsidized at low income): $150-$300
• Everything else: $350-$500

No restaurants, no travel, limited entertainment. Lean FIRE works for people who genuinely prefer simple living, own their home outright, or live in low cost-of-living areas. It falls apart in expensive cities or with unexpected medical expenses.

The hidden Lean FIRE advantage: At $30,000/year income from portfolio withdrawals, your federal tax rate is near zero. Long-term capital gains at that income level are taxed at 0% federally. Many Lean FIRE retirees pay little to no federal income tax.

What Fat FIRE Actually Looks Like

$120,000 per year is $10,000 per month. This funds:

• Housing (own or rent premium unit): $2,500-$3,500
• Groceries plus dining: $1,200
• Transportation (car plus travel): $1,000
• Healthcare (private, comprehensive plan): $1,500-$2,000
• Travel (2-3 international trips per year): $1,000/month averaged
• Entertainment, shopping, giving: $1,500

Fat FIRE maintains the lifestyle most high earners are accustomed to. The tradeoff is time: reaching $3 million takes significantly longer than $750,000.

Time to Reach Each Number (From $0)

Assuming $100,000 household income, 7% real returns, spending as noted:

| FIRE Type | FIRE Number | Savings Rate Needed | Years to FIRE | |-----------|-------------|--------------------|-| | Lean FIRE | $750,000 | 30% ($30,000/yr) | 17 years | | Regular FIRE | $1,500,000 | 40% ($40,000/yr) | 22 years | | Fat FIRE | $3,000,000 | 20% ($20,000/yr) | 47 years |

Fat FIRE at $100,000 income with $120,000/year spending is mathematically impossible without income growth. Fat FIRE typically requires either very high income (earning $300,000+ and saving $150,000+/year) or starting with significant assets.

The Coast FIRE Bridge

Many Fat FIRE chasers use a Lean FIRE bridge. They retire early on Lean FIRE terms, do part-time or semi-retire work they enjoy, and let the portfolio grow to Fat FIRE levels while spending is partially covered by income.

At $1,500,000 invested at 7% real return, the portfolio grows by $105,000 per year. Spend $60,000, earn $20,000 part-time, and the portfolio still grows $65,000 per year. In 10 years, it hits $2.7 million without additional contributions.

Which FIRE Type Should You Target?

Ask three questions:

1. What is the minimum monthly budget that would feel like a good life? That is your Lean FIRE floor. If the answer is $5,000/month, Lean FIRE at $750,000 is too lean for you.

2. What does your ideal retirement day look like? Travel, hobbies, and dining out scale the budget quickly. A retired life that looks like your current life costs what your current life costs, minus work expenses, plus healthcare.

3. How much longer would you work for each level? The marginal year of work going from Regular to Fat FIRE is years of your life. Quantify the trade-off.

Frequently Asked Questions

Can Lean FIRE work in a high cost of living city?

Rarely. $30,000 per year in San Francisco, New York, or Boston does not work without unusual arrangements (paid-off housing, below-market rent, shared housing). Lean FIRE typically requires relocating to a lower cost area domestically or internationally.

What is the difference between Fat FIRE and just being rich?

Fat FIRE is about having enough invested that the portfolio generates your lifestyle without working. Being rich means having high income. High earners with $150,000 income and $140,000 in spending have a 43-year path to Fat FIRE despite the impressive salary.

Should I aim for Fat FIRE or invest the extra years?

Some of both. Financial planners often recommend targeting Chubby FIRE ($2-2.5 million), which funds a comfortable life without requiring the extreme savings rate or timeline of Fat FIRE. The difference between comfortable and lavish retirement is often small in day-to-day happiness but large in required portfolio size.