In the case of joint assessment, both spouses file a joint tax return. The income of both spouses is first added together and then divided in half. The income tax is calculated for the divided taxable income, which is then doubled again. This taxation procedure, also called spousal splitting, particularly favours married couples with large income differences, because it results in a lower average tax rate.
If, on the other hand, the income of both spouses is approximately the same, there is no advantage in adding up the incomes and applying the splitting tariff compared to taxing the spouses separately.
The requirement for joint assessment is that the spouses are married to each other, have unlimited tax liability and live together for at least one day of the year.
If you do not select an assessment type on the tax return form, the tax official will automatically apply a joint assessment.