The present invention relates to a tool and a method for creating back tapers at an internal or external toothing of a gear. The tool rotates during use about a tool axis of rotation includes a tool shaft extending along the tool axis of rotation, a fastening section for fastening the tool to a tool drive of a machine tool, the fastening section formed at an end of the tool shaft, and at least one cutting blade, which is arranged at a fastening position provided at the circumference of the tool shaft. The tool according to the invention and the method according to the invention enable with simple means the creation of geometrically precisely shaped back tapers at toothings without the need for the use of specially shaped cutting inserts or a change of machine tools proven in practice for the creation of back tapers. This is achieved according to the invention in that the diameter of the tool shaft measured in a plane oriented normal to the tool axis of rotation increases starting from the diameter, which the tool shaft has at the fastening position of the cutting blade, in a direction directed towards the fastening section.