The tried-and-true guideline for when to ditch your running shoes is after 300 to 500 miles, but seriously, who’s keeping track? For help, we turned to Warren Greene, editor (and shoe expert) at Runner’s World magazine. His advice: Look to the heel—specifically, the foam under the heel of the shoe. “That foam is smooth on new shoes,” Greene says. “If yours shows deep wrinkles, similar to the wrinkles on your knuckles, get a new pair.” Then look to the bottom. If the tread has smoothed or you can see bits of the foam through the sole, you’re past due for new shoes.

What about “barefoot running” shoes? “On these, the cushioning doesn’t really wear out because there’s no cushioning to begin with,” says Greene. Replace them when the sole starts to wear away or the upper material begins to crack.