There’s no hard-and-fast rule about when it’s a good time to retire your boots, or how long they should last. 500 miles walked on concrete will wear soles down more quickly than 500 miles out on the hills, and anything from the way you walk to how well they’re looked after can affect their longevity, with different materials and soles wearing at different rates too.
Forking out for a replacement pair unnecessarily is not only bad for the environment, it's bad for your bank balance too. Equally, struggling on in shoes that have seen better days could damage your feet. Worn or damaged soles can even be dangerous as they won’t offer you the grip you need to stay safe, so it’s important to know what signs to look out for.