I have a beard. I've found that having one affords me the advantage of only shaving every other day. When I shaved it off for a few years, I had to shave every day and changed blades more often, though I don't really pay attention to how often. I also alternate between a Mach 3 and a sensor 3. I use either of those for the general part of the shaving in the large areas. For finer tuning near the edges of my beard, I use the old sensor excel two-blade. It actually is tougher to shave when one has a beard because of this. But I guess it evens out with not having to shave every day. since I alternate the Mach 3 and sensor 3 every month, I'd guess I change wither every 3-4 months. So, let's say I change each after a 1 1/2 month use. With every other day, that comes to about 3 weeks. That's my guess. On a related topic, don't forget to change your toothbrushes every 3 months. And use soft bristles.