FIRE: financial independence explained

FIRE (Financial Independence, Retire Early) is the movement that proposes accumulating enough invested wealth for its returns to cover your living expenses indefinitely. It's not just for the wealthy or for Silicon Valley. With the right numbers and a disciplined strategy, it's an achievable goal — though it requires adaptation to your local context.

Your FIRE number = Annual expenses × 25 (based on the 4% rule)
The 4% rule says you can withdraw 4% annually from your portfolio without depleting it over 30 years
With annual expenses of €18,000 you need a portfolio of ~€450,000
Three types of FIRE: Lean FIRE (reduced spending), Regular FIRE, Fat FIRE (premium lifestyle)
FIRE is achievable on average incomes — it requires a savings rate of 40–50%, not a six-figure salary

What is the FIRE movement

The modern FIRE concept was popularised by the book 'Your Money or Your Life' (1992) and went mainstream through the Mr. Money Mustache blog from 2011. The core idea: if you save and invest aggressively for 10–15 years, you can accumulate enough wealth to live off its returns for the rest of your life without needing to work for money.

The important nuance: FIRE is not necessarily about stopping work. It's about having the freedom to choose. Many FIREd people continue working on what they love, do volunteer work or start businesses — they just no longer do it out of financial obligation.

The 4% rule: the mathematical foundation

The Trinity Study (1998) analysed historical portfolios in the American markets over 30-year periods and concluded that a portfolio invested in equities and bonds can sustain a 4% annual withdrawal without being depleted in 95% of the historical scenarios analysed.

This gives the FIRE formula:
Wealth needed = Annual expenses ÷ 0.04 = Annual expenses × 25

Examples:
- Expenses of €12,000/year → you need €300,000
- Expenses of €18,000/year → you need €450,000
- Expenses of €24,000/year → you need €600,000
- Expenses of €36,000/year → you need €900,000

Caution: the Trinity Study uses American data. For horizons beyond 30 years (if you retire at 40) or portfolios with more bonds, some planners recommend using 3–3.5% for greater safety.

The three types of FIRE

Lean FIRE: living on very reduced expenses (under €15,000/year in Spain or equivalent). Requires the smallest portfolio (~€375,000) but implies an austere lifestyle. Works best in rural areas or small cities with a low cost of living.

Regular FIRE: the average lifestyle you'd have while working (€18,000–30,000/year). The most common target for families. Portfolio needed: €450,000–750,000.

Fat FIRE: maintaining a premium lifestyle without restrictions (~€40,000+/year). Requires over €1M. Typically only achievable with high income or very aggressive accumulation over a long time.

Is FIRE achievable on an average income?

The average net salary in Spain is around €1,500–1,800/month (€18,000–21,600/year). With that income, Lean FIRE or Regular FIRE is achievable — but requires a savings rate of 40–50%, which means significantly reducing expenses.

A realistic scenario for a couple in Spain with combined net income of €3,000/month:
- Expenses: €1,800/month (€21,600/year)
- Monthly savings: €1,200 (40% rate)
- FIRE target: €21,600 × 25 = €540,000
- With €1,200/month at 7% per year: reached in ~22 years

Starting at 30, they would reach FIRE at 52. Not retirement at 35, but financial independence at an age when many people still have 13 years of compulsory work ahead.

Practical steps to get started

Step 1 — Calculate your FIRE number: track your annual expenses carefully. Your number = annual expenses × 25.

Step 2 — Know where you stand: calculate your current net worth (assets minus liabilities). The gap between your current wealth and your FIRE number is the distance to cover.

Step 3 — Maximise your savings rate: the savings rate is the most powerful lever. Going from 10% to 30% savings rate cuts your time to FIRE almost in half.

Step 4 — Invest consistently: compound interest needs time. A global equity ETF (VWCE, IWDA) with monthly contributions is the standard approach.

Step 5 — Build multiple income streams: salary, rental income, dividends, side projects. Diversifying income accelerates the path and provides resilience once you reach FIRE.

Frequently asked questions

What is my FIRE number?

The invested capital that could cover your annual spending with sustainable withdrawals. With the 4% rule, 25 times your annual spending.

Is FIRE possible on an average salary?

It is slower, but possible with a high and consistent savings rate. Many people aim for partial independence first.

What types of FIRE are there?

Lean (very low spending), Fat (high spending), and Barista or Coast (part-time income, or letting the portfolio grow without new contributions).

How do taxes affect FIRE?

Withdrawals may be taxed, so calculate your number on after-tax spending. Tax-advantaged accounts can reduce the capital needed.

Read further

Your Money or Your Life (Vicki Robin and Joe Dominguez). It gives you: Helps you decide how much is enough and spend by your priorities, which almost no other book works on.
The Simple Path to Wealth (JL Collins). It gives you: Turns index investing into a complete, simple plan all the way to financial independence.
Die With Zero (Bill Perkins). It gives you: Adds the view missing from almost every saving book: what the money you build up is for.