If you marry, you will automatically be placed in tax class IV at the time of the marriage if

• you are not permanently separated and
• your domicile or usual place of residence is in Germany.

The registry office automatically informs the Federal Central Tax Office of the marriage.
Alternatively, you can apply for the formation of the tax class combination III/V. Furthermore, you can choose the tax class combination IV/IV with factor.

Your employer or the employer of your wife or husband should not be informed of the change in marital status? If so, you or your wife or husband can apply to your tax office for tax class I to be taken into account. The effect with regard to the wage tax deduction then corresponds to tax class IV. Alternatively, you can have your employer block the retrieval of the electronic wage tax deduction characteristics.
If you do this, however, your employer is obliged to tax your wages according to the least favourable tax class VI.

Background information on tax class choices by married couples:
The employer usually only knows the wages of the employee working for him, but not those of the wife or husband. Consequently, only the wages of one employee can be taken as a basis for the wage tax deduction of the other employee. The wages of both spouses can only be combined after the end of the year within the framework of the income tax assessment. Only then does the correct annual tax result. It is therefore often unavoidable that too much or too little income tax is withheld during the course of the calendar year. In order to come as close as possible to the annual result, spouses can choose between 2 tax class combinations (IV/IV as the statutory rule and III/V on application) and the factor method.
Which tax class combination is the best? This cannot be answered in a general way, but depends on your needs and the circumstances of the individual case.

Combinations IV/IV or III/V:
The tax bracket combination IV/IV assumes that the spouses earn approximately the same amount. The tax class combination III/V is designed in such a way that the sum of the tax deductions for both spouses is approximately equal to the joint annual tax if the wife or husband with tax class III earns 60 percent and the wife or husband with tax class V earns 40 percent of the sum of the earned income of both spouses. As a result, the tax deduction for tax class V is proportionately higher than for tax classes III and IV. This is also due to the fact that in tax class V the basic allowance for the subsistence minimum is not taken into account, but is taken into account in double the amount in tax class III. If the ratio of actual wages does not correspond to the legal assumption of 60:40, this can lead to back tax payments. For this reason, there is an obligation to submit an income tax return when choosing the tax class combination III/V.

Combination IV/IV with factor:
Instead of the tax class combination III/V, you can choose the factor procedure in addition to the tax class combination IV/IV. The tax class combination IV/IV in conjunction with the factor to be calculated by the tax office ensures that the basic tax-free amount applicable to each wife and husband is taken into account when deducting income tax by applying tax class IV and that the income tax to be withheld is reduced by applying the factor of 0,... (always less than 1) in accordance with the effect of the splitting procedure. The factor is a tax-reducing multiplier that is calculated from the effect of the splitting procedure if the spouses' wages differ. Allowances are included in the factor. The factor is automatically provided to the employer as an electronic wage tax deduction feature.

Notice:
Since the law introducing the right to marry for persons of the same sex came into force on 1.10.2017, new civil partnerships can no longer be formed in Germany. Same-sex couples have been able to enter into marriage with each other since this date and are thus on an equal footing with opposite-sex couples.
Existing civil partnerships can be converted into a marriage. However, there is no obligation to do so. Existing civil partnerships can be continued in their previous form.