TLDR: If you get married or enter into a PACS, you are in principle taxed jointly for the entire year concerned. However, you may opt for separate taxation of your income, under the conditions provided for by the CGI.
The joint taxation rule
If you get married or enter into a PACS, joint taxation applies in principle to the entire year in which the event occurs. It is therefore not limited to the period after the date of the marriage or PACS.
It covers all income you received during that year. For partners bound by a PACS, joint taxation is assessed in both your names.
The tax household return
A single comprehensive income tax return is filed for the tax household. It must include the income of its members, in accordance with the rules applicable to joint taxation.
You sign the return jointly with your spouse or partner. However, a return signed by only one of you remains enforceable against the other.
The option for separate taxation
For the year of the marriage or entry into a PACS, you may waive joint taxation and opt for separate taxation of your income.
Each assessment then covers the income you personally received during the year, as well as your share of the jointly received income. If this share is not substantiated, the jointly received income is divided equally between you.
You must exercise this option within the deadline provided for filing the initial income tax return referred to in Article 170 of the CGI. The option is irrevocable. It does not apply when you were already bound by a PACS entered into for a previous year and subsequently marry each other.
Special situations
If you were already bound by a PACS declared to the tax authorities on 1 January of the year of the marriage, the marriage has no effect on your household’s withholding tax rate and you do not have to declare the marriage for withholding tax purposes.
Furthermore, for withholding tax purposes, married persons who have separate property regimes and do not live under the same roof continue to be taxed separately. This rule concerns the application of withholding tax and does not alter the general rule set out above.