Your brakes should generally be replaced every 50,000 miles. Unfortunately, there is not a set number of miles or amount of time after which they should be changed. Your driving habits will ultimately determine how often they need to be changed. For example, someone who has driven 50,000 miles in the flatlands will not need to change their brakes as often as someone who drives in a crowded urban area. You must also take into consideration your own driving habits such as how harshly your brake.
You brakes will often tell you when they need to be changed by emitting a squeaking noise. Do not ignore the signs. If your brakes are making a squeaking or grinding noise, make sure that you bring them to us for repair or replacement.