To ensure that the income tax withheld is as close as possible to the expected income tax, employees are assigned to different tax classes according to their personal circumstances. You can have the tax class stored as ELStAM changed at your tax office. A tax class change can only be made with effect from the month following the application.
In the case of marriages during the calendar year, the tax class combination IV/IV is automatically created for spouses. The spouses can jointly apply to change the automatically formed tax class combination IV/IV to III/V or IV/IV with factor (§ 39f EStG). In this case, the change of tax class - in contrast to the usual cases of changing the tax class combination - takes effect from the beginning of the month of marriage or from the first day of the month of marriage.
You are obliged to have the tax class and the number of child allowances changed by the tax office if the entries differ from the actual circumstances, for example because the spouses/partners are permanently separated and the requirements for tax class III have therefore ceased to apply.
This obligation also applies if tax class II is certified, but the conditions for taking into account the relief amount for single parents no longer apply in the course of the calendar year.