Berlin uses zones A, B and C. Most city journeys need AB; BER Airport and Potsdam sit in C, so a trip between central Berlin and the airport needs ABC.
The zone map in three lines
The airport test
If the journey begins at BER and ends in central Berlin, buy ABC. An AB ticket covers the city but not the airport in zone C. The same ABC logic applies whether you use the Airport Express, regional train, S-Bahn or connecting local transport.
The stamp is part of the ticket
Paper tickets from station machines generally need validation at the small yellow or red boxes. On S-Bahn and U-Bahn, stamp before boarding. Tickets bought directly on buses or trams may already be validated, so read the ticket rather than stamping twice.
Digital means activate, not merely own
A ticket stored in a BVG app must be activated before the journey unless its product rules say it starts automatically. A screenshot, purchase confirmation or inactive ticket is not a valid substitute during inspection.
One way for 120 minutes
A Berlin single ticket is valid for 120 minutes in one direction and allows transfers and interruptions. It does not permit a return trip or a circular sightseeing ride back toward the starting point.
Why the small step matters
Travelling without a valid ticket can lead to an increased fare of EUR 60. An unstamped paper ticket may look paid-for in your hand, but BVG treats it as invalid.