FIRE & Independence

Lean FIRE vs Fat FIRE Calculator

Compare lean and fat FIRE targets side by side with lifestyle-adjusted timelines and withdrawal safety.

Decision Summary

Years between Lean and Fat FIRE

10 years

Lean FIRE: $750,000 (10y). Fat FIRE: $2,000,000 (20y).

Scenario Comparison

The main answer and the most important supporting outputs in one glance.

Years between Lean and Fat FIRE

10 years

Lean FIRE number

$750,000.00

Fat FIRE number

$2,000,000.00

Years to Lean FIRE

10 years

Key Metrics

Lean FIRE number

$750,000.00

Fat FIRE number

$2,000,000.00

Years to Lean FIRE

10 years

Years to Fat FIRE

20 years

Lean FIRE progress

26.67%

Fat FIRE progress

10.00%

How to use it

Enter current portfolio, annual savings, expected return, lean annual spending, and fat annual spending. Lean FIRE covers essentials only while fat FIRE funds a comfortable lifestyle, so be honest about where your real spending falls.
Read lean FIRE target, fat FIRE target, years to each, and the gap between them. The difference in years is usually large because fat FIRE targets can be 2-3x lean targets, and the extra portfolio takes time to compound.
If lean FIRE is 5 years away but fat FIRE is 15, you face a real tradeoff between early freedom with constraints and later freedom with comfort. Most people underestimate how much they will spend once work is optional.
Decide which version matches your risk tolerance, then set intermediate milestones. Coast FIRE or barista FIRE can bridge the gap between lean and fat if you are willing to earn part-time income. Run those calculators next.
Re-run annually or after major spending changes. Track years-to-lean, years-to-fat, and whether your actual spending is drifting toward the fat number.

AI Integrations

Contract, discovery endpoints, and developer notes for agent use.

Always available for agents

Tool contract JSON

https://aifinhub.io/contracts/lean-fire-vs-fat-fire-calculator.json

Stable input and output contract for this exact tool.

Human review

People can use the browser page to sense-check outputs and charts, but agents should still execute against the contract and discovery endpoints.

/agent-tools.json - machine-readable tool index.
/llms.txt - human-readable model discovery guide.
/.well-known/webmcp.json - WebMCP capabilities manifest.
/.well-known/ai-plugin.json - plugin-style discovery manifest.

{
  "tool": "lean_vs_fat_fire",
  "lean_annual_spending": 32000,
  "fat_annual_spending": 80000,
  "current_portfolio": 275000,
  "annual_savings": 36000,
  "annual_return_percent": 7,
  "withdrawal_rate_percent": 4
}

Open tool contract JSON Open AI integrations guide

Expand developer notes

Agent playbook

Resolve Lean FIRE vs Fat FIRE Calculator from /agent-tools.json and open its contract before execution.
Validate inputs against the contract schema instead of scraping labels from the page UI.
Open the browser page only when a person wants to review charts, assumptions, or related tools.

Agent FAQ

Should ChatGPT, Claude, or another agent click through the UI?

No. Start with /agent-tools.json, then follow the tool's contract URL. The page UI is for human review, not parameter discovery.

When do tools show Quick and Advanced?

Every tool opens in Quick Start first. Advanced Controls keeps the same scenario, reveals more assumptions or diagnostics, and every tool keeps AI integrations inline below the instructions.

When should an agent still open the browser page?

Open it when a human wants to sense-check the output, review the chart, or keep exploring related tools after the calculation finishes.

Questions people usually ask

What is the difference between Lean FIRE and Fat FIRE?

Lean FIRE targets minimal annual spending (typically $25K-$40K/person) for the earliest possible retirement. Fat FIRE targets a comfortable or even luxurious lifestyle ($80K-$200K+/year). The portfolio required for Fat FIRE can be 3-5x larger, adding years or decades to the accumulation phase.

How does this calculator compare the two paths?

It models both scenarios in parallel using your current savings, contribution rate, and expected returns. You see two timelines, two target portfolio sizes, and the year gap between achieving Lean FIRE and Fat FIRE — helping you decide where your comfort threshold lies.

Is Lean FIRE actually sustainable long-term?

It can be, but it leaves little margin for unexpected expenses like medical emergencies, inflation spikes, or lifestyle changes. Many Lean FIRE retirees find they need to supplement income after a few years. Build a buffer above your minimum for resilience.

When should I use this vs the standard FIRE calculator?

Use this when you are deciding between retiring earlier with less versus later with more. The standard FIRE calculator models a single target. This tool forces you to confront the tradeoff between time and lifestyle.

Is my data stored?

No. All calculations happen in your browser. Nothing is stored or transmitted.