If you are receiving an income from employment in the Netherlands, your employer will always deduct wage tax from your salary. This is the general tax on income that every citizen in the Netherlands is obligated to pay.
However, this deduction of taxes does not take into account any deductible items or tax credits that you might have. This means that in some cases, you have paid too much tax. At the end of the year, you can request a refund of this excess amount by filing for an income tax return. Instead of receiving this at the end of the year, you can also obtain a refund before this. You can request the Dutch tax office to pay you the excess amount in monthly instalments.