Whether or not you have to pay taxes in Germany depends on the funding of your work contract and the duration of your employment.
Research scholarships are tax−free when they comply with the following conditions:
The organization granting your scholarship will be able to tell you whether you have to pay tax on your scholarship or not. A "tax−free" status also exempts you from paying social security contributions. Nonetheless, you must still show a proof of health insurance.
If you are employed by the University for more than 6 months (min. 183 days) you will have to pay taxes and social security contributions. Both will be deducted from your salary and transferred directly to the state by your employer. The amount of taxes you pay depends on your income, your family situation and your tax category (Steuerklasse). If you stay in Germany for less than 6 months, your income will be taxed in your home country.
In order to ensure that foreign citizens are not taxed twice, both in their home country and in Germany, so-called double taxation agreements (Doppelbesteuerungsabkommen, DBA) have been negotiated with 75 different states. Departing from the 6-months rule mentioned above, the double taxation agreements with some countries rule that for example international visiting scholars who come to Germany for a maximum of 2 years to do research in public research institutes can pay their taxes in their home country. You can find out which countries this applies to (EU member states and some other states) and which other tax regulations need to be taken into account under the following addresses.
You need to apply for a wage tax card (Lohnsteuerkarte) when you register at the Einwohnermeldeamt. You must hand this over to the personnel department of Bielefeld University. At the end of the calendar year, either this Lohnsteuerkarte or a computer printout of the accounting data will be returned to you. You have to hand this over to your Finanzamt together with your tax declaration (Steuererklärung).
On your Lohnsteuerkarte, you will find your tax category (Steuerklasse). This is related to your family status, how many children you have, and whether or not your marriage partner is also employed. The amount of tax you pay depends on your level of income and your Steuerklasse.
In Germany, the state collects church taxes (Kirchensteuer) together with income tax for the major churches in the country (9% of income tax). Please report your church affiliation to the Einwohnermeldeamt when they are preparing your Lohnsteuerkarte. If you are not a member of a Protestant or Roman Catholic Church, you do not have to pay Kirchensteuer.