As a FreeFlexer you have to declare your income tax, as well as your turnover tax.

Income tax
Everyone registered and working in the Netherlands is obliged to declare their income taxes. If you’re under contract, your employer will have filled in your tax declarations for you. If you work as a FreeFlexer, you are solely responsible for calculating the amount of taxes you have to pay. Be sure to calculate your total income and its taxes each year, before the first of May. You can find more information on the income tax here. 

Turnover tax
As a FreeFlexer it’s likely that you will need to declare your turnover taxes. This depends on whether you are participating in the new small businesses scheme. If you don’t sign up and participate in this regulation, you will declare your taxes every quarter, so 4 times a year. You do this by filling in your income and expenses online. After which you can deduct certain VAT from the amount of VAT you earned.

Tip: download the app Btw-Alert offered by the Tax Authorities and always receive a reminder when you have to declare your turnover tax.