In principle, your income tax class also changes when you marry. After the registration of the marriage by the registration office, you and your spouse/life partner will initially be automatically assigned tax class IV in the new electronic ELStAM(Elektronische LohnsSteuerAbzugsMerkmale) procedure. Consequently, you will also receive tax class IV (and not III) if your spouse is not in an employment relationship. If you want tax class III to be taken into account, you must apply for this on the official form Antrag auf Steuerklassenwechsel bei Ehegatten/Lebenspartnern (Application for change of tax class for spouses/partners) at the tax office responsible for your place of residence. You can also submit the application electronically under "My Elster". Authentication is required for this.
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Note on ELStAM:
The characteristics relevant for the wage tax deduction procedure, such as tax class, factor if applicable, number of child allowances, other allowances, but also the church tax characteristic are stored by the tax authorities for all employees in a central database. On the basis of this data, the tax authorities make the wage tax deduction characteristics available to employers for electronic retrieval.
In principle, the tax offices are the point of contact when it comes to changing tax classes or other wage tax deduction characteristics.
The municipalities continue to be responsible for the administration of registration data, e.g. marital status, marriage, birth, entry into or exit from church. This means that the tax authorities can only form the ELStAM correctly if you meet your legal obligation to register and the municipalities can send the relevant data to the tax authorities. You can find more information on this topic at www.elster.de.