How often should you change spark plugs?

how often do spark plugs need to be changedHow often should you change spark plugs?
going by a normal maintenaince schedule-

30,000 miles for standard plugs

100,000 miles for platinum and iridium

but its the responsible thing to do to replace the platinum and iridiums at65k-75kHow often should you change spark plugs?
change once a year or if the motor starts running bad
it depends on the plugs. i have bosch platinum + 4 plugs with198,000 miles on them and they run fantastic!
Most plugs are good for 100,000 miles unless car starts to run bad or has decrease in fuel mileage.
on newer cars most of them recommend 100,000 miles but you better check your owners manual.