A synchronous belt with trapezoidal shaped teeth operating on an involuted (undercut) pulley is analyzed for contact stress by a direct finite element approach. The belt-pulley geometry difference is mathematically accounted for during the belt deformation process. Both an idling and loaded automotive camshaft belt are considered. Peak stress is shown to exist in the belt tooth root. Drive parameters, pulley diameter, belt tension and tension difference are varied around application conditions. The degree of pulley undercut is shown to have a significant effect on peak, stress for a loaded belt (9.525 mm pitch, 25.4 mm wide) on an 18-tooth pulley (56.562 mm pitch diameter).