Normally get around 1500 miles on the road. Depending on how clean I keep- it the MTB will get 1,000 miles or less.

It's that keeping clean that will get more mileage from chains. I have a chain cleaning tool and as soon as I see the rear cassette getting stained with black oil from the chain- I clean the chain. Can be after each ride in wet weather or 3 to 400 miles if the conditions are right. Just as important is chain lube. In Dry summer I use a dry lube. Doesn't attract dust from the road but will get washed off if it is shown any moisture.