Child support attorneys in United States help the mother or father determine their rights and responsibilities for financially supporting a child. In many cases, the non-custodial parent pays support to the custodial parent under child support calculations mandated by state law. The child support calculators use factors such as income, expenses, and time-sharing arrangements. When the circumstances of the parent or child change significantly, one parent can go back to modify the child support order. Family law and divorce attorneys that represent parents in child support cases typically require a retainer and base their attorney fees on an hourly rate.