A turbine or compressor blade assembly includes a blade fixed to a dovetail section attachable to a wheel. The dovetail section has a dovetail shaped to fit in a correspondingly shaped slot in the wheel. A dovetail platform serves as an interface between the blade and the dovetail. An undercut fillet radius is formed at an intersection of the dovetail platform and a dovetail pressure surface, where the undercut radius has a multi-part profile shape configured to attenuate edge of contact stresses. An additional feature is the area where the undercut radius transitions into the P-cut area at the forward end (leading edge) of the dovetail.