Can I take my bike with me free of charge with the day ticket for Germany?

To take bicycles with you, you need one all-day bike ticket per bicycle.

Exceptions:

This does not apply to routes where special conditions apply that allow holders of DB tickets to transport bicycles for free. Please contact the respective associations and regional units for more information.
If you can fold your bike and pack it easily in the luggage racks at your seat, you can take it with you as free hand luggage.