This depends on the car, the brake system, and the car owner's driving habits. Typically, a car's brakes should be replaced after about 50,000 miles, but some car's brakes may last anywhere from 25,000 to 70,000 miles.
Car owners shouldn't wait for a magic number to replace their brakes. They should check them regularly, and pay close attention if they hear any weird noises or if the car feels shaky while braking. Brakes are a critical safety component of a car, so it's important to stay on top of brake maintenance.