A method for assisting a coupling process of a transportation vehicle reversing toward a trailer which includes detecting a ball head coupling of the trailer based on a camera image recorded by a camera of the transportation vehicle, limiting the camera image to an image detail in which the ball head coupling is disposed, detecting at least one curved front edge of the ball head coupling within the limited image detail, and determining the engagement position fir a vehicle-side ball head based on the at least one detected curved front edge of the ball head coupling. A trailer coupling assistant for a transportation vehicle.