A putting guide assembly and its associated method of use. The putting guide assembly attaches to the head of a putter. The putter head has a striking surface for striking a golf ball. The putting guide assembly is attached to the putter and presents a flexible guide surface that extends forward of the putter's striking surface. The flexible guide surface can be configured into different curvatures. As the flexible guide surface is adjusted, the perceived curvature observed by a golfer holding the putter changes. A golfer can therefore selectively change the perceived curvature to match the natural curvature inherent in that golfer's putting swing.