Depending on your situation, you must complete Form 163 (annual statement) or Form 100 (tax return). You must choose Form 100 if, for example: Your household's taxable income is more than €100,000 Some of your income is not subject to withholding tax. E.g. rental income, ... You own your own home and have mortgage interest to deduct Non-residents/frontier residents: you have special expenses (insurance, ...) or extraordinary fees to deduct If none of these cases fit your situation and the Tax Administration has not specifically asked you to return Form 100, then choose Form 163