truthfully
it all depends on driving style and braking efficency
i almost never need to change my pads and i have slotted rotors which eat pads for breakfast lunch and dinner
i brake only with enough force as needed
and early,
when stopped i release on the brake to just hold the car stopped ,not pressing all tehy way right down
which helps keep the pads cooler
one reason why my rotors look very clean
no warpage or grooves
i actually had one person ask me if i chromed them
because they are so clean and reflective looking
on average i would say 40 000 miles but that is a guess