Starting with €10,000 and investing €300 a month at a 6% return and 0.3% yearly fees gives about €148,500 after 20 years once an estimated €11,000 of Dutch box 3 tax is deducted. You would have deposited €82,000, so growth after fees and tax is roughly €66,000.
How does investing a fixed amount each month work?
Each month you buy a slice of, for example, a global equity fund with a fixed amount. You buy more units when prices are low and fewer when they are high, and the returns build on themselves through compounding. This calculator takes your expected annual return, subtracts the yearly fees and grows the portfolio month by month. It is a model with a constant return, whereas real markets swing sharply. Use it to compare scenarios, not to predict the future. Dutch readers know this as the beleggen calculator.
Why fees matter so much
A fee of 0.3% looks tiny, but it is charged every year on a growing pot. At a 6% return over 20 years, 0.3% in fees costs about €8,500 of the final value in the example above. At 1.5%, which some actively managed funds and robo-advisers charge, the gap is far larger. Always compare the ongoing charges figure (OCF) and the broker’s transaction costs.
Box 3 and your investments
The Netherlands taxes private investments on a deemed return in box 3, not on actual gains. For 2026 the deemed return on investments is 6%, the rate is 36% and the tax-free allowance is €59,357 per person. That works out to about 2.16% of your wealth above the allowance each year. When you tick the option, the calculator deducts that every year, assuming one person with no savings, partner or debts. For an exact figure use the Box 3 Calculator. From 2028 the government plans to move to tax on actual returns.
Tips for a realistic projection
- Use a cautious return, for example 4% to 6% for global equities over the long run.
- Test a scenario with 0% growth and one with a 20% drop in the first years.
- Do not invest money you will need within five years.
- Compare with saving, using the Compound Interest Calculator, and with repaying a mortgage, using the Mortgage Repayment Calculator.
To measure what your investments returned so far, use the Investment Return Calculator, and for share income try the Dividend Calculator.
How to use this calculator
- Enter your starting amount and monthly deposit.
- Choose an expected return and the yearly fees of your fund or broker.
- Tick the box 3 option to include an estimate of Dutch wealth tax.
- Press Calculate and read the year-by-year table of your expected portfolio value.
Key figures at a glance
| Box 3 investments 2026 | 6.00% deemed return, 36% rate |
|---|---|
| Allowance | €59,357 (€118,714 with a partner) |
| Costs to compare | OCF plus transaction costs |
Frequently asked questions
It depends on your goals and risk tolerance. A common approach is to build an emergency buffer first and then invest an amount you can leave alone for years.
For global equities, 4% to 7% a year over the long term is often used, with large swings along the way.
You pay 36% on a deemed 6% return on assets above €59,357, regardless of what you actually earned.
Fund costs (OCF), transaction costs, broker service fees and sometimes currency costs.
No. Values can fall and you can lose money. Diversify and invest only what you can afford to leave.