hat is impossible to answer. you replace them when they are worn and it will vary alot from one make to the other.for instance i had 2 f350 fords and 1 3500 dodge and 1 3500 chevy, the 2 fords would wear the brakes out in about 18 months. the chevy went over 3 years on the original brakes and the dodge went 4 years. now keep in mind these trucks were being used commercially so the brakes did get used alot, all of these truck were towing scaffolding and construction equipment

Brake rotors don't have an expiration date or a scheduled replacement. They are replaced when they are worn down to the wear limits established by the manufacturer.

Whenever they are warped or worn to the point of minimum thickness.

How often that is depends on where you drive ( highway vs. urban driving for example ) and how hard you are on your brakes.

Tell Cletus to measure them at the next brake pad replacement.

When they have wear patterns which machining them can't fix, or worn beyond min. thickness.