How often do I need to regrade the ground around my house?
Regrading isn't typically a recurrent necessity. It may be needed shortly after a home is built, and maybe again a few years later. However, eventually the soil becomes compacted to the same degree that the undisturbed adjacent soil is, and that's more or less the end of the story. Then it's a matter of whether rainwater flows adequately away from the foundation. 

Simply put, it varies by home, depending on home age, roof design, soil type, contractor technique, climate, ant proliferation, and other factors. There are no rules of thumb or other guidelines.