Sneakers are definitely having a fashion moment. That said, it’s important to remember that your beloved Adidas commuter sneaks aren’t made for the gym. Gym shoes, on the other hand, are designed for function first — your workout!

So, with more styles and specializations than ever, how do you know when it’s time to ditch your treads and buy a new pair (or two or three)? The answer depends primarily on your typical workout. Follow this guide to find when it’s time to chuck your workout shoes for new kicks.

Is your idea of a workout walking to get your daily coffee every morning? The good news is that your sneakers will stand the test of time for a long while.

There are four main components of athletic shoes that can break down or wear out: the outsole, midsole, heel counter, and shank, according to the American Academy of Podiatric Sports Medicine. Your fashion sneakers won’t likely experience excessive abrasion on the outsole, shank, or heel.

That said, you should keep an eye on your midsole, which is normally composed of a shock-absorbing foam material. The amount worn is the most crucial impact on this part of the shoe. If you’re walking in these shoes every day, they’re still at risk of overuse.

If you press on the foamy part of your shoe, does it compress or rebound? If not, it’s time to step out in a new pair or risk alignment and overuse injuries.

Swap ’em out: Every three to five months if you walk 45 minutes at least three times a week.

Do you have a long relationship with the elliptical machine at the gym? Your sneakers will likely stay in fine shape for a while, so long as you buy the appropriate pair to begin with.

Elliptical machines are designed to be low-impact and flexible, with the ability to target similar muscles to running when going forward. But they also target totally different muscles (your glutes and hamstrings) when going backward.

If you mix it up on the machine, then you’ll want to buy cross-trainers. They’re more versatile and protective for both forward and backward movements. “A cross-training shoe that is comfortable with ample width in the toe box would be the best bet,” says Mike Scaduto, a physical therapist for Champion Physical Therapy and Performance in Massachusetts.

Swap ’em out: Every 6 to 12 months, depending if you’re mostly working out indoors or outdoors and your level of impact.

You’ve done a few 5Ks (maybe when there’s beer involved). Especially if you’re just starting out, Scaduto recommends a thorough assessment by a qualified professional to ensure proper fit, including individual foot type and running style. If your running is style more occasional than every day, assess the midfoot for signs of wear and tear as early as three months into running.

Try this formula

  • Physical therapist Mike Scaduto uses this formula to figure out when to replace running shoes: 75,000/body weight (lbs.) = miles you can run before replacing.
  • For example, if you’re 150 pounds, you’re looking at replacing your running shoes at about 500 miles.

Swap ’em out: Every 300 to 500 miles, or when you start to notice signs of wear and tear.

Who needs other shoes? You live in your sneakers. The best bet is to have completely separate sneakers for any other activity you do, as your running shoes are going to be getting a lot of traction and action.

Even if you got into running because it’s less expensive than other sports, use common sense once your shoes start breaking down — even if it’s sooner than you thought. “They aren’t doing what they’re designed to do anymore, and may be detrimental to your body,” Scaduto says.

Set yourself up for success with healthy sneakers and healthy feet. Same goes for people who wear toe shoes — look for obvious signs of degradation and replace them as soon as the midsole, heel, or shank isn’t standing up on its own.

Swap ’em out: Follow the formula above, and plan to get new shoes every 300 to 500 miles or when you start to notice signs of wear and tear.

Monitoring our footwear in all sports and activities is important. Not only that, but supporting the feet properly keeps you moving ahead — as well as setting a safe base for your spine, posture, and muscle development. Running can be one of life’s simple pleasures, so take a breath and enjoy those new shoes.

Lindsey Dodge Gudritz is a writer and mom. She lives with her on-the-move family in Michigan (for now). She’s been published in The Huffington Post, The Detroit News, Sex and the State, and The Independent Women’s Forum blog. Her family blog can be found at Putting on The Gudritz.