Yes, a Deutsche Bahn BahnCard functions as a subscription and will automatically renew for another year unless you cancel it in writing. This applies to the standard BahnCard 25, 50, and even the "My BahnCard" for young travelers. To prevent the renewal, you must submit your cancellation at least six weeks before the end of the current term. If you are using a "Trial BahnCard" (Probe BahnCard), the deadline is often shorter, typically requiring cancellation six weeks before the three-month trial ends. You can cancel through your "My Bahn" account on the website, via a contact form, or by mail. If you miss the deadline, the card is extended for a full year at the standard price, so it is highly recommended to set a calendar reminder as soon as you purchase one.