I'm giving my xdh until March to pay child support. If he doesn't (which I doubt he will) then I am going to go file for child support through the state. Will they take back child support for when he was not paying or from the date I file?
In our state, it is just from the date you file.
Every state has it's own specific laws. Your best bet is to ask somebody where you live.
Almost all states will hit him for back CS plus add 12% monthly interest so he will be screwed. The state will also take his income tax until he is caught up.
from the date you file, they can... sometimes even before that.. it really all depends.