Each year, you must file a personal income tax return. This return can be filed individually or jointly.
In Belgium, tax rules vary depending on your family situation as of January 1st of the tax year, whether you are single, married, or in a legal cohabitation.
Understanding when and how to complete a joint tax return is essential to avoid mistakes and optimize your taxes. Here's what you should pay attention to :
You need to distinguish between different situations:
👫 If you are married:
Your marriage took place before January 1st → you will have to file a joint return.
Your marriage took place after January 1st → you will have to file a separate return that year, and then a joint return the following year.
🏡 If you are legal cohabitants:
You entered into legal cohabitation before January 1st → your return will then be joint.
You entered into legal cohabitation after January 1st → your return will be separate that year, and then joint the following year.
❌ De facto cohabitants
De facto cohabitants do not need to register administratively and have no legal obligations toward each other.
Even after several years together, a joint return is not possible.
🧭 Key takeaway: ✅ It is your marital status on January 1st of the tax year (the year in which you file your return and are taxed) that determines whether your return will be joint or individual. 💡 Only married couples or legal cohabitants can file a joint return. ⏰ January 1 is a public holiday → plan your administrative procedures in advance! |
💬 Most common cases:
👤 You are... | 📅 Your situation on January 1st | 📄 Type of declaration | ✅ What you must do |
| Doesn’t matter | Individual | File alone. |
| Married before January 1st | Joint | One single declaration for the couple. |
| Married after January 1st | Separate | Each files their own declaration. |
| Cohabitation before January 1st | Joint | You are treated as a married couple. |
| Cohabitation after January 1st | Separate | Each files their own declaration. |
| Doesn’t matter | Individual | No joint declaration possible. |
📌 Special cases:
📌 Situation | 🧾 Type of declaration | ℹ️ Useful detail |
|
|
Unless already separated on 1 January. |
| Separated (following year) | Each person files separately. |
| Joint (year of death) | The declaration covers the entire year. |
| Individual (following year) | You declare as single. |
When you file a joint tax return, you can benefit from a specific advantage: the marital quotient.
💡 Tip: The marital quotient is especially useful when there is a significant income imbalance between the spouses. |
If one spouse has little or no income and the other earns significantly more, up to 30% of the combined net professional income can be allocated to the spouse with little or no professional income.
This mechanism applies: |
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This allows for better use of tax brackets, thus reducing the total tax payable.
Here’s a concrete example:
Spouse 1 earns €45,000 of taxable income, and Spouse 2 earns €0 of taxable income.
Married couple + Spouse 2 earns less than 30% of the combined income → the marital quotient can be applied.
Possible transfer: 30% of Spouse 1’s income, with a maximum of €13,460 (cannot transfer more than this).
Income after transfer to the second spouse:
Spouse 1: €31,540 (€45,000 − €13,460)
Spouse 2: €13,460 (€0 + €13,460)
Result: The couple pays less tax because their incomes fall into lower tax brackets compared to a normal distribution.
ℹ️ Important to know with Accountable ℹ️With Accountable, only the part of the tax return related to self-employed income (part 2) is prepared for you! The first part must be completed separately by the non-self-employed spouse. 👉 For the joint tax return to be valid and submitted, both parts (the self-employed part and the spouse’s part) must be completed and filed together in a single submission via Tax-on-web. When completing a joint declaration, the older person's details are entered in the left-hand column and the younger person's details in the right-hand column. |
Do you have any other questions or need more information? Feel free to contact us via our chat! 📩
Author - Valesca Wilms
As content marketing lead at Accountable Belgium, Valesca writes about freelancing, self-employment, and taxes based on her own experience as a freelancer.
Who is Valesca ?Thank you for your feedback!
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