A safety razor blade can last anywhere from 3 to 10 shaves, depending on a few factors such as the thickness of the stubble, the coarseness of the hair, and the quality of the blade itself. However, it is always important to replace the blade as soon as it starts to drag or pull on the skin, as this can cause nicks, cuts, and irritations. Using a dull blade can also lead to bacterial infections and ingrown hairs. In general, it is recommended to change the blade once a week if you shave daily, or once every two weeks if you shave less frequently. Proper storage and maintenance of the razor can also help prolong the lifespan of the blade.