Tax disadvantages through progressive taxation
Normally, the individual taxable income of private individuals is classified in a progression table and taxed at the rate of that tax class. But for married couples, income isn't considered individually for taxes, but added together. Since the tax rate increases for each class in the table, a higher percentage of tax from taxable income is charged per class. So married couples, who are taxed together, naturally fall into higher classes in the progression, as their salaries are added together. In a fictitious example, a couple who would each pay 10% of their taxable income in taxes on the basis of individual taxation would pay more tax at a 15% rate through joint taxation.
The marriage penalty actually means that for dual-income couples where both partners earn 75,000 to 125,000 francs annually, there is an added tax burden of around 10% compared to cohabiting couples with the same income.