How much do I need to retire in Spain? The FIRE Number Calculator

Have you ever stopped to calculate exactly how much money would allow you to send your boss away and never work again? In the FIRE (Financial Independence, Retire Early) movement community, this number has a mystical name: the FIRE Number.

For most people starting out in planning for financial independence, the answer seems quick and simple: multiply your annual expenses by 25 and that’s it. If you spend €24,000 a year, you need €600,000. End of conversation.

However, if you live in Spain, strictly applying this rule is an almost guaranteed recipe for long-term insolvency. Because? Because that rule was designed in the hallways of an American university and does not take into account our most persistent and silent partner: the Tax Agency (AEAT). In Spain, the impact of personal income tax on savings income and the characteristics of our cost of living require an adapted calculator.

In this article, we are going to mathematically break down how much you really need to retire early in Spain in 2026, integrating the tax toll and the real cost of living numbers.

The origin of calculation: The rule of the multiplier by 25

Before adding the Spain factor, it is essential to understand the scientific basis of this calculation. The FIRE number is derived directly from the 4% Rule, formulated following the famous Trinity Study published in 1998 by Trinity University, Texas.

The researchers analyzed the historical behavior of mixed portfolios of stocks and bonds in the United States from 1926 to 1995. Their conclusion was that an initial withdrawal rate of 4% of capital, adjusted annually for inflation, allowed the money to survive a minimum of 30 years without going to zero in practically all historical retirement periods.

Mathematically, the inverse of withdrawing 4% annually is multiplying your annual expenses by 25.

$$\text{FIRE Number} = \text{Annual Expenses} \times 25$$

If your goal is to cover monthly expenses of €2,000 (€24,000 per year):

$$24,000\ \text{€} \times 25 = 600,000\ \text{€}$$

If you manage to accumulate €600,000 invested in a long-term diversified portfolio, traditional mathematics tells you that you can withdraw €24,000 the first year, update that figure with inflation the second, and your assets will survive.

But this is where we collide with the reality of Spanish taxation.

The tax trap in Spain: Net expenses vs. gross withdrawals

When the Trinity Study talks about “annual expenses,” it assumes that your investments are in American tax-advantaged accounts (such as Roth IRAs or 401k) where capital gains may be exempt or heavily subsidized.

In Spain, on the other hand, every time you sell a share of your index funds or your shares to pay for food, electricity or rent, the Treasury claims its part of the capital gains. In 2026, the tax base of personal income tax savings is taxed according to the following progressive brackets:

The myth of 21% taxes on all money withdrawn

A common mistake among beginners is to think: “Well, if I need €24,000 net a year to live, I will have to pay 21% personal income tax, so I have to withdraw about €30,000 from my portfolio”.

This is not correct due to how asset sales are taxed in Spain. You do not pay taxes on the total amount of money you withdraw, but only on the capital gain (the gain).

Imagine that for 15 years you have been contributing monthly to a global index fund that replicates the MSCI World. After years of compound interest, your portfolio is worth €600,000, but of that figure, €300,000 corresponds to your own capital contributed from your salary (on which you already paid taxes at the time) and another €300,000 are the capital gains generated by the market. This means that your portfolio has 50% accumulated profit.

If you need to withdraw €24,000 in your first year of retirement:

• €12,000 corresponds to the original capital you invested (tax exempt).
• €12,000 correspond to capital gains subject to personal income tax.

The Treasury will calculate the taxes on those €12,000 of profit:

• The first €6,000 is taxed at 19% = €1,140
• The next €6,000 is taxed at 21% = €1,260
• Total tax payable: €2,400

To get your net €24,000 in the bank, your total gross withdrawal will have to be €26,400 (€24,000 for you + €2,400 for the AEAT). The effective withdrawal rate on your accumulated €600,000 will not have been 4.0%, but 4.4% due to the tax impact. If the market suffers an initial down year, that 0.4% of fiscal friction can dramatically accelerate your portfolio’s risk of bankruptcy.

The Real FIRE Number Calculator in Spain (Net vs. Gross)

To counteract this fiscal toll, we must recalculate our FIRE Number based on three typical spending profiles of Spanish families.

In the calculations below, we assume a mature index fund portfolio with an estimated average capital gains ratio of 65% of total capital at retirement (a realistic scenario after 15-20 years of constant accumulation).

Comparative Table of Real FIRE Capitals in Spain

Note: The previous calculations estimate the application of capital gains withholding using the FIFO (First In, First Out) system and assuming a latent capital gain of 65% of the portfolio.

As the table demonstrates, the fiscal reality in Spain pushes the necessary multiplier progressively. Instead of 25 times expenses, an investor in Spain should aim for a multiplier of between 28 and 29 times their annual net expenses if they want to retain a margin of safety equivalent to that of the original study.

Strategies to reduce your FIRE Number by optimizing your taxes

It’s not all bad news. Spanish legislation offers very powerful tools for smart investors to minimize their tax bill in the withdrawal phase:

1. Tax deferral of Investment Funds

Unlike investors in ETFs (common in the rest of Europe and the US), in Spain we have transferability of investment funds. You can move your money from an equity index fund (like an MSCI World) to a money fund or bond fund without having to pay a single cent in taxes in the process. This allows you to rebalance your portfolio for free to suit your risk needs.

2. Smart withdrawals with FIFO rule and cost basis

When selling shares, the law requires you to apply the FIFO criterion (the first shares you bought are the first you sell). As the first contributions you made 20 years ago are those that accumulate the highest percentage of capital gains, the tax burden will be greater in the first years of your retirement.

You can cushion this if you maintain portfolios in different investment funds or financial entities purchased at different times, allowing you to strategically sell shares with lower accumulated capital gains if you need to cross a bear market bump.

3. The combination with other “flavors” of FIRE

If you manage to diversify your sources of income using dynamic strategies such as Coast FIRE or the Barista FIRE, you will be able to keep your withdrawals from the variable income portfolio to an absolute minimum, allowing your tax base to always remain within the first bracket of 19% of personal income tax.

How to simulate your real FIRE Number in My FIRE Simulator

A traditional spreadsheet cannot dynamically calculate market swings combined with progressive tax toll. To model your particular case with complete rigor, we recommend using our free Monte Carlo simulator.

Follow these simple steps to analyze the viability of your number:

1. Access the application: Open the My FIRE Simulator.
2. Define your expenses: Enter your desired net expenses in the left panel. To be as close to taxes as possible in Spain, we advise you to increase your estimate of annual expenses by 12% or 15% (by entering the “Estimated Annual Gross Withdrawal” figure that corresponds to you from our comparison table).
3. Choose the calculation engine: Switch between the “Monte Carlo Simulation” tab (which will create 10,000 random walks based on variance and mean returns) and the “Historical Data” tab to test your plan against real crises like the Great Depression of 1929 or Japan’s lost decade of the 1990s.
4. Analyze the 10th Percentile: In the results, do not look only at the average success percentile. Review the 10th Percentile (worst 10% of market scenarios). If your capital survives in that unfavorable percentile with the simulated withdrawal rate, you have found your safe FIRE Number in Spain.

Conclusion: Numbers don’t lie

Calculating your number for financial independence in Spain is an exercise in realism. Multiplying your expenses by 25 is a fantastic starting compass for staying motivated during your first few years of saving. However, when you get closer to the date of taking the leap into the void, you should replace the compass with a high-resolution map.

Adjusting your number to the Spanish personal income tax rate (raising it towards the range of 28-30 times your net annual expenses) and simulating your plan against storms of inflation and volatility using the My FIRE Simulator is the only way to ensure that your early retirement is truly permanent and worry-free.

Time is your most valuable resource. Protect your plan, do the real math, and secure your future.

This article is exclusively educational and informative in nature. It does not constitute personalized financial, tax or legal advice. Past returns do not guarantee future returns. Always consult with a registered wealth advisor before making major decisions about your capital.

My FIRE Simulator

Creator of My FIRE Simulator and index investing enthusiast. My goal is to help you achieve financial freedom with math and no false promises.