TL;DR: Log in to your “Public Finances” account, open “File my income tax return,” check the pre-filled information, add any missing details, then sign your return.
Who must file an income tax return
Anyone liable for income tax must submit a detailed return to the tax authorities. You must state your income and profits, your family circumstances and the other information needed to calculate your tax.
If you are married, you must jointly sign your household’s overall income tax return.
Accessing your online account
To file online, log in to your “Public Finances” account using your tax number and password.
If you do not yet have a password, use your tax number, online access number and reference taxable income. If you have forgotten your tax number or password, recovery procedures are available from the authentication screen.
For a first online tax return, if you are at least 20 years old and have received a letter from the tax authorities informing you of this possibility, use the codes provided in that letter to create your password.
Checking the pre-filled information
After identifying yourself, select “File my income tax return.” Your return is pre-filled with the information known to the tax authorities.
Check your family circumstances, address and the amounts shown. You can correct the pre-filled data before continuing.
Completing the return
Add any other income you received, as well as the expenses, tax reductions and tax credits to which you are entitled.
For your family circumstances to be taken into account, provide the surname, first names, date and place of birth of each of your children and dependants.
The return must also include, where applicable, capital gains subject to tax deferral, tax-exempt capital gains provided for by law and the information needed to calculate your reference taxable income.
Signing, confirming and correcting the return
Sign your return online for it to be taken into account. After submitting it, you immediately receive a confirmation email, and an acknowledgment of receipt is available in your “Public Finances” account.
You can correct your return even after signing it.