This question always comes up at insurance renewal time. Our car is 9 years old and has driven 65000 miles, so I'm planning to tell them the mean average of 9500 miles a year. But of course some years I drive more than others, and that's difficult to predict - I drove hardly any in 2020 due to Covid, and well above average in 2021 because my terminally ill parent lived 350 miles away. In general, we expect the annual mileage to go down significantly over coming years, because our children are becoming less reliant on lifts.
Do you just use the average, or do you try and predict what you will use in the year ahead? (The mileage is recorded on the MOT certificate, so the insurance company can check the accuracy of the predictions if they want to).
Also, how do you determine who is the "main driver"? I drive the car most frequently, but DH always drives if we're going somewhere together, and they're usually longer trips, so he definitely does more miles in it than me.