Originally Posted by Drew Eckhardt

I usually replace rear shift cables every 2000 miles to prevent breakage at 2200 - 2600 miles, but shift more when I'm out of shape and had issues at 1301 (broke completely) and 1558 (broken strands) miles. The last one made it to a normal 2186 miles.

That's every 10 weeks riding a lot, and still less than annually when barely riding.

Combining shifters level with the bar tops and under tape cable routing added a tight ninety degree bend which doubled cable fatigue and cut life in half. Moving away from the flying housings caused the same problem with Shimano mechanical shifters.

How that translates into mileage varies with how much you shift.