Many members will tell you how they lost a shoe size when they lost weight. Unfortunately, I am not one of those members. My feet just seem to keep getting bigger ! LOL !!!
Depending on how much use your shoes get, figure they should be changed about every 3-4 months. If you only use them at the gym and not outside, they could last a bit longer. Buy a couple of pairs and rotate them. That's another way to get them to last longer.
However, once the support does wear out, it's time to buy new ones.