In Germany, service is usually included in your restaurant bill, but it is widely considered appropriate to give a 10 percent tip, or Trinkgeld in German (which translates as “drinking money”).
The question is not only how much to tip, but also how to tip. Don’t leave your tip on the table, but give it to your waiter when you pay. The easiest way is to round the sum of the bill up and include the tip. For example, when your dinner costs 27 Euro, just give the waiter 30 Euro even.
If you are feeling bold, try a little German and say Stimmt so (pronounced shtimt zo, meaning “we are even”), and your waiter knows that gratuity is included.