While I do track mileage on my shoes via Strava, like others here, I really don't think there's a solid rule of thumb on miles. I have had shoes from the same brand vary widely in the mileage I could get out of them. For me, it has typically been anywhere between 300 and 600+ miles. I find that, if I listen to my feet and my knees, I go off that to determine when to retire shoes. I also like to rotate through a couple different pairs of varying styles. Yep, I am shoe nerd (as much as I can afford to be anyways). 

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