A gear unit for a powertrain and a powertrain including a stepped planetary gearset, a first gear shifting element and a second gear shifting element. The stepped planetary gearset has a first sun gear, a first ring gear, a second ring gear, and stepped planet gears rotatably mounted at a first planet carrier. The first ring gear is fixed with respect to rotation to an output shaft of the gear unit. The second ring gear is fixed with respect to rotation to a housing. The first gear shifting element drivingly connects the first sun gear to an electric machine in a closed state, and the second gear shifting element drivingly connects the first planet carrier to the electric machine in a closed state, and one of the two gear shifting elements is in the closed state for driving the output shaft in rotation.