When is it mandatory to file an income tax return (IB) in the Netherlands?

When is it mandatory to file an income tax return (IB) in the Netherlands?

If you receive an invitation to file from the tax authority
In this case, filing the return is always mandatory.

If you have to pay additional tax (usually above €51)
For example, due to additional income, insufficient tax withheld, or box 3 assets.

If you are an entrepreneur (sole trader, VOF, etc.)
As an entrepreneur, filing a return is always mandatory.

If you have income from abroad
For example, salary, pension, or assets.

If your assets in box 3 exceed the tax-free threshold
For example, savings, investments, or a second property.

If you have multiple sources of income
For example, multiple employers or a combination of employment and business activities.

If you have income on which no or too little tax has been withheld
For example, freelance income.

When is it not mandatory, but often advisable?

If you have not received a notice and are likely entitled to a refund
In this case, you can file voluntarily, which is often beneficial.