A rotor blade for a flow machine, in particular a steam turbine, includes an insertion root with a first finger and two second fingers which are arranged on either side of the first finger in axial direction. The first finger and the second fingers have a shoulder in axial direction on axial sides facing one another such that the fingers have a radially outer first portion and a radially inner second portion whose axial extension is shorter than that of the outer, first portion. In relation to a total axial width between axial sides of the two second fingers which face away from one another, the radial height of the first, radially outer portion is in the range of 0.39 to 0.45, particularly 0.40 to 0.44, and the radial height of the second, radially inner portion is between 0.40 and 0.46, particularly between 0.41 and 0.45.