In general, we estimate each blade lasting for about 5 shaves; however, this is highly dependent on the density and thickness of whatever is being shaved, be it a grizzly beard or very fine leg hair.
With that said, we use the following guidelines:
Low Shaving Frequency (1 or 2X per week): 3 Blade Packs per Year
Medium Shaving Frequency (2 - 4X per week): 4 -5 Blade Packs per Year
High Shaving Frequency (5 -7X per week): 7 -10 Blade Packs per Year