This depends on the specific model you buy and how frequently you use your electric razor, but in general, most brands recommend replacing the blades every 12 to 18 months. How your razor feels when you're shaving can also be an indicator of when to replace it. If your electric razor feels rough, doesn't create as close of a shave as it used to, pulls at your hair, or you start to see irritation in the shaved areas, it's time to replace your blades.