When you apply the brakes in your car, the brake pads make contact with the brake's rotor, which slows down the vehicle. Over time, the pads wear down from repeated contact with the rotor. As your brake pads wear down to their limits, you may begin to hear grinding or screeching.
The speed of brake pad deterioration depends on driving habits, the vehicle and the quality of the brake pads. Having them checked periodically will ensure that your car always has healthy brake pads. Mechanics typically check brake pad wear during routine maintenance and vehicle tune-ups.
While the specific amount of time your brake pads will last depends largely on the varying factors, RepairPal.com strongly suggests replacing brake pads whenever 25 per cent or less of them is left. It is never a good idea to rely on the squeaking, grinding or squealing noises. These are signs that you've already waited too long. Rely on periodic checks by your mechanic instead.