Travel calendar – foreign workdays
If you are not living in the Netherlands but you do have a Dutch employment contract then you are in most situations only taxable in the Netherlands on the days you actually work in the Netherlands. A travel calendar can be used to calculate for which days you have to pay Dutch tax.
A travel calendar can also be used if you have the US nationality or US greencard and the 30% ruling is granted to you. In this situation you also only have to pay tax on days actually spent in the Netherlands.