When should I pay an income tax supplement?

Your tax return (made in the spring) allows you to calculate the final amount of tax due in respect of your income from the previous year.

For example, your return in spring 2026 calculates the tax due for 2025.

If the tax calculated from the return corresponds to the withholding taxes made in the previous year, your tax is paid. You don't have to do anything.

If the tax calculated from your return is higher than the total of the levies made in the previous year, you still have to pay additional tax.

There are several reasons for this discrepancy, including the following:

• Your income has gone up and you haven't asked change your collection rate
• You touched a advance of tax reductions or credits too high.

The tax supplement (balance) to be paid is indicated on your tax notice.

The tax supplement is taken from your bank account in one of the following ways:

• Up to €300 : in 1 time in September
• More than €300 : in 4 times from September to December.

In addition to the top-up tax, you continue to pay your withholding tax for the current year.

For example, you pay the additional tax due for 2025 and the withholding tax due for your 2026 income.

If you have difficulty paying the additional tax, you can request a payment deadline.

Video - Withholding tax: why do I have a balance to pay?

If the tax calculated from your return is less than total levies you paid too much income tax in the previous year.

The tax authorities must reimburse you for the overpayment.

There are several reasons for this discrepancy, including the following:

• Your income went down and you didn't ask change your collection rate
• You are entitled to more tax reductions or credits than the previous year.

The overpayment to be refunded is indicated on your tax notice.

The refund is fired on your bank account during the summer.

For example, if you paid too much tax for 2025, the overpayment is refunded to you in the summer of 2026.