fatfire calculator

What is FatFIRE?

FatFIRE is a financial independence target that supports a high-comfort lifestyle in retirement, often with significant discretionary spending for travel, dining, housing, hobbies, and generosity. Unlike LeanFIRE or standard FIRE, FatFIRE plans for more cushion and flexibility rather than a minimal budget.

In practical terms, people often define FatFIRE by annual spending levels such as $150,000, $200,000, $300,000 or more, depending on location and lifestyle. The right number is personal: your FatFIRE target should reflect your desired life, not someone else’s spreadsheet.

How the calculator works

1) It estimates your target portfolio

The core formula is:

If you want to spend $200,000 per year and use a 3.5% withdrawal rate, your baseline target is about $5.71 million in today’s dollars.

2) It adjusts your spending for inflation

If retirement is years away, your future spending need will likely be higher. The calculator compounds your spending target using your inflation assumption, then computes a future-dollar FatFIRE number.

3) It projects portfolio growth

Your projection uses your current portfolio, expected annual return, and yearly contributions. The output shows your estimated portfolio at retirement and whether you have a surplus or shortfall versus your target.

How to choose good assumptions

Withdrawal rate

• 3.0%–3.5%: more conservative, common for longer retirements or uncertain markets.
• 4.0%: classic rule of thumb, but may be aggressive for very long horizons.

Return and inflation

• Use a moderate long-term return estimate instead of best-case performance.
• Don’t set inflation to zero. Even low inflation has a big effect over 15–25 years.

Spending target

Be honest about your desired life. A realistic FatFIRE plan includes healthcare, housing maintenance, travel, gifts, and optional luxuries. Underestimating spending is one of the most common planning mistakes.

Example scenario

Suppose you target:

• $220,000 annual retirement spending
• 3.5% withdrawal rate
• $750,000 current portfolio
• $90,000 annual contributions
• 7% annual return, 2.5% inflation, 14 years to retirement

Your future-dollar target will be meaningfully higher than the simple “25x” quick estimate. This is exactly why scenario planning matters: inflation plus timeline can change the required portfolio by millions.

How to improve your FatFIRE odds

• Increase investable savings: even an extra $1,000/month can materially reduce your gap.
• Protect downside risk: diversify and avoid overconcentration in one stock or one sector.
• Delay retirement by 1–3 years: more compounding, fewer withdrawal years, often a huge difference.
• Use dynamic spending: flexibility in down years can improve portfolio sustainability.
• Account for taxes: mix taxable, tax-deferred, and tax-free accounts intelligently.

Common mistakes with FatFIRE planning

• Assuming a high return and low inflation at the same time.
• Using gross income instead of actual spending needs.
• Ignoring one-time costs (home upgrades, family support, major travel years).
• Forgetting sequence-of-returns risk during the first retirement decade.
• Treating your first calculation as final instead of revisiting annually.

Final thoughts

A FatFIRE calculator is not a prediction machine; it is a decision tool. Use it to test trade-offs: save more, retire later, lower target spending, or combine approaches. The best plan is one you can execute consistently through both strong and weak markets.

Re-run this model whenever your income, spending, market outlook, or timeline changes. Small adjustments today can create major optionality tomorrow.