child support is to support the basic needs of the children, based on the incomes of both "homes" - some families will have a mum doing it tough, dad on big income, so a large amount of child support. some will be the other way around, and no child support will change hands. the calculation takes into account how much time the children spend with each parent, the income of both parents and all that stuff. it's not supposed to cover a certain expense - it's there to "support" the children based on the means of the parent paying child support