What is the FIRE movement and financial independence

What is financial independence?

Financial independence is the point where you have enough invested capital to cover your expenses from its returns, without depending on a salary¹. It is not the same as being rich: someone with modest expenses needs far less than someone with an expensive lifestyle. What matters is the relationship between what the portfolio earns and what you spend.

The FIRE movement, short for Financial Independence, Retire Early, popularised a concrete way to get there: save and invest a high share of your income for some years, until the capital you build up is enough to live off the returns. The "retire early" part is optional: many people keep working, but with the freedom to choose.

The 4% rule and your "independence number"

The centrepiece of FIRE is the 4% rule. It comes from a US study (the Trinity study) that looked at how much you could withdraw from a diversified portfolio without running out over a 30-year retirement. The practical conclusion: about 4% a year, then adjusting that amount for inflation.

From that comes your financial independence number (or "FI number"):

FI number = annual expenses ÷ 4% = annual expenses × 25

For example, if you spend €1,500 a month, that is €18,000 a year. The capital you need is €18,000 ÷ 0.04 = €450,000. From there, withdrawing 4% (€18,000) covers, on average, a year of expenses.

You do not have to do this by hand. Our financial independence calculator works out the FI number and estimates how long it takes to reach it from your savings and expected return.

Your savings rate matters most

The factor that most influences the time to independence is not your return: it is your savings rate, the share of your net income you manage to invest every month. Saving more does two things at once: it speeds up how fast capital builds and lowers your expenses, reducing the number you need.

Take the calculator example: at 30, with €10,000 already invested, €1,000 of monthly savings, a 5% real annual return and €1,500 of expenses, you reach €450,000 in about 20 years and 5 months, at around age 50. You save €255,000 and compound interest provides the other €197,000. Raising your monthly savings visibly shortens that timeline.

Always use a real return

When projecting over the long term, reason in real return, that is, with inflation already removed. For long-run global equities, the historical real return is around 4% to 5% a year. Working in real terms keeps everything in today’s euros: the FI number and the time to reach it stay in current purchasing power, with no separate inflation adjustment. Our investment return calculator shows nominal value and real value side by side.

Flavours of FIRE

Not everyone pursues the same goal. There are several "flavours":

• Lean FIRE: independence with low expenses, so a smaller FI number.
• Fat FIRE: a more comfortable lifestyle, which requires a bigger portfolio.
• Coast FIRE: you already have enough invested that, on growth alone and with no further contributions, the portfolio reaches the FI number by retirement age. From then on, your salary just needs to cover current expenses.
• Barista FIRE: you cover part of your expenses with part-time work and the rest with the portfolio.

FIRE in Portugal: what to keep in mind

The maths is universal, but some national details matter:

• Taxes. In Portugal, capital gains on shares and funds are generally taxed at an autonomous rate of 28%². The 4% rule assumes gross figures, so it is worth using a slightly lower return or a slightly larger FI number to leave room for tax.
• The public pension still exists. Despite the "retire early" label, the years you contribute to Social Security still count towards your old-age pension. FIRE complements the public system, it does not replace it.
• The 4% rule is a reference, not a law. It was calibrated on US data and 30-year retirements. For someone who "retires" very early, the horizon is longer, which argues for a more prudent withdrawal rate such as 3% to 3.5%.

How to get started

You do not need a complex strategy to take the first step:

1. Know what you spend. Your independence number depends on your expenses, so knowing your budget is the starting point.
2. Set a sustainable savings rate and automate your saving every month.
3. Invest in a diversified, long-term way, with a prudent return expectation.
4. Track your progress instead of trying to time the market.

Try your own figures in the financial independence calculator and see, year by year, how far you are from your number. The goal is not to predict the future to the cent, but to understand the order of magnitude and make decisions with realistic expectations.