Similar to the concept of fuel usage varies according on where and how you drive, the same thing applies for the brake pad. The brake pad life span will depend on multiple factors.
For example, if you are driving only 12000km per year, but mainly in the congested area, there is a possibility that you will need to replace the brake pad more often compared to someone that is driving 45000km per year.
Unfortunately, there is no specific scheduled can be used as a guide to change the brake pad. Therefore, normally most people just rely on your hearing sense or the advice of an experienced automotive technician. Besides that, since most car need their tires to be rotated and balanced every 6 months, that would be the best time to get the brake pad inspected as well.
Mechanic would be able to check the thickness and condition of the brake pad. Most car equipped with wear sensor which scraps the disc brake once the brake pad layer need to be change. Driver usually would be able to hear screeching noise whenever they pressed the brake pedal.
However, not all vehicle is equipped with the sensor, thus the driver need to be alert with any squeaking, squealing or any other noises that appeared whenever they pressed the brake pedal. This could indicate that it is time to change the brake pad.
Some of the noises can be remove by cleaning the brake. Hence, if the noises still continue after you have clean your brake, it can also indicate that the brake pad has worn out. Other indication might be experience thumping when pressing the brake pedal or taking longer time for the car to fully stop.
Service your car with SERV and get free 22 checkpoints inspection to know the condition of your brake pads.