After deregistration at the local government office, you must also request a final taxation document from your local tax office. After you leave Belgium you have three months to complete the document and send it back. This will put an end to your tax duties in Belgium. Make sure you include your new international address so that the final calculation can be sent to you. You might need this document for tax purposes in your new country or if a double tax treaty is applicable.
The ‘special’ status of the final taxation document will be marked on the first page. The year will be shown and the ‘special’ box will be ticked.