How often does a hermit crab change shells?

When ever a hermit crab grows out of its old shell it finds a new one to call home.
There is no set amount of times a hermit crab will change its shells. The hermit crab will only change shells if it has grown to big for its original one. Otherwise, the hermit crab will not change shells. It all depends on the hermit crab's growth rate and size.