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📈 Financial simulator

Compound Interest Simulator

Visualize the power of compound interest: initial capital, regular contributions, interest reinvestment.

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Enter your parameters and click "Calculate" to visualize your capital growth.

⚠️ Disclaimer — For indicative purposes only: The results obtained via the tools and simulators on this site have indicative value only and have no legal, tax or accounting value. Calculations are based on the legal provisions in force at the date of their last update and are subject to change. La Caverne de la Compta makes every effort to keep this data up to date but cannot guarantee its accuracy or completeness. La Caverne de la Compta cannot be held liable for any direct or indirect damages resulting from the use of the information obtained. The user is solely responsible for decisions made based on simulation results. Consult an accountant, tax advisor or notary before making any decision. La Caverne de la Compta is not a licensed financial, tax or legal advisor and the information published does not in any way constitute personalised advice. — Full legal notice

Compound interest in Belgium: FIRE strategy, ETFs and withholding tax

Compound interest is one of the most powerful wealth-building mechanisms over the long term. In Belgium, every investor must however factor in the specific tax treatment for a realistic projection.

Belgian withholding tax: 30% on your financial income

Most financial income in Belgium (dividends, interest, capital gains on certain products) is subject to a 30% withholding tax. Use the "Tax" toggle in our simulator to see the real impact on your final capital and compare gross vs net scenarios.

The 4% rule and FIRE strategy in Belgium

The 4% rule (Trinity Study) states that a portfolio can sustain a 4% annual withdrawal for at least 30 years without depletion. In Income mode, our simulator precisely calculates the capital needed for your desired monthly income, factoring in the net rate after withholding tax.

Concrete example: To receive €1,500/month from an ETF portfolio at 7% gross with 30% tax (4.9% net rate), you need a capital of €367,347. Without tax at 7% gross, only €257,143. The difference is significant — our simulator gives you the exact figure.
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❓ Frequently asked questions about compound interest in Belgium

What is the 4% rule in Belgium ?▼

The 4% rule (FIRE strategy) states that you can withdraw 4% of your capital annually without depleting it long-term. In Belgium, you must account for the 30% withholding tax on financial income, which reduces the real net withdrawal rate.

What is the withholding tax on interest in Belgium in 2026 ?▼

The Belgian withholding tax is 30% on most financial income. The first 1,020€ of interest on regulated savings accounts is exempt. This simulator automatically accounts for this deduction in all calculations.

What is the difference between simple and compound interest ?▼

Simple interest is calculated only on the initial capital. Compound interest is calculated on capital plus accumulated interest, creating exponential growth. At 5% over 20 years, 10,000€ gives 20,000€ with simple interest versus 26,533€ with compound interest.

How do you calculate the capital needed to live off income in Belgium ?▼

Divide your desired monthly income by the annual net yield after withholding tax, then multiply by 12. Our simulator has an income mode that automatically calculates the capital needed to generate X€ per month.

Are ETFs subject to withholding tax in Belgium ?▼

Accumulating ETFs do not trigger withholding tax on reinvested dividends. Capital gains on sale are generally tax-exempt for Belgian individuals. Distributing ETFs pay dividends subject to 30% withholding tax.

What to invest in to benefit from compound interest in Belgium?▼

Main options: accumulating ETFs (automatic reinvestment, no withholding tax on reinvested dividends), branch 23 life insurance (withholding tax exemption after 8 years), regulated savings account (€1,020/year exempt). Accumulating ETFs are often preferred for maximum compounding effect without tax friction.

Which bank or platform offers the best compound interest in Belgium in 2026?▼

Traditional Belgian banks offer low savings rates. For maximum compound interest, investors turn to brokers like Bolero, Keytrade, Trade Republic or DEGIRO to buy accumulating ETFs (e.g. IWDA, VWCE). Trade Republic and Revolut also offer interest on deposits, but without the long-term compounding effect of an ETF.