A comfortable and supportive pair of shoes are a runner’s best friend, but even the best aren’t built to last forever. Avid runners know working out in worn-out sneakers can cause unwanted running injuries like shin splints or runner's knee. But how do you know it’s time to trash your sneaks and invest in a new set? Here, two running experts share the signs that cue a much-needed trip to your local shoe store.

You’re racking up miles

“As a rule it’s best to update your running shoes every 300 to 400 miles,” says Nikhil Jain, senior footwear product line manager at Brooks Running. Since wear and tear on the shoe itself isn’t always obvious, this method ensures you get new shoes before your worn ones cause pain or an injury.

You can easily track your runs with apps such as Strava, MapMyRun, or Wahoo, or with a fitness tracker. You could also opt for an old-school approach and hand write your runs in a journal. If you’re looking to eyeball your mileage based on time, take advice from a pro: New York City-based running coach John Henwood says he replaces his own shoes every two months.

You feel aches and pains

“As soon as one of my runners feels a shin splint, the first thing I do is ask them how long they’ve had their shoes for,” says Henwood. Knee pain and shin splints, which cause pain in the lower part of the leg, could both signal you need new shoes, especially if you haven’t changed up your running routine at all.

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Not ready to part with your precious sneakers? Jain suggests keeping them around for leisurely walks or running errands. “While they may no longer be in good condition to run in, it’s likely that you won’t need as much cushion and support in your other activities,” he says.

Your shoes look shabby

According to Henwood, there are three areas on the shoe itself that signal it’s time for a replacement: the sole, the tread, and the exterior fabric.

“The cushioning in your shoe will be the first thing to break down because midsoles are designed to absorb shock and protect the body,” says Jain. “The tricky part is that this wear isn’t easily visible.” If the soles are shot, the shoe may appear lopsided from putting more pressure on one part of your foot than the others.

The tread of the shoe will be the next area to wear out, so if the bottom of the shoe appears flat and smooth, chances are your soles have lost their support and cushioning. Any holes that appear in the shoe’s exterior fabric provide a third red light that they’ve deteriorated.

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To prevent your shoes from wearing out before you hit 300 to 400 miles, Henwood suggests using them exclusively for your runs. “If you’ve got running shoes, don’t walk around in them,” he says. “Have your running shoes for running and other shoes for walking because how you use them changes how they last.”

Jain also suggests rotating between two pairs of running shoes to prolong each pair’s life. “In addition, having more than one running shoe in your rotation helps you work a slightly different set of muscles in your feet, helping you strengthen them,” he says.