Money paid to the parent with the child custody is called child support. This alimony and support is to pay for reasonable needs of any children for health, education and other maintenance.
Usually, the total income of both parents with consideration of fixed expenses such as car payments, utilities, mortgage, etc, is considered in determining the dollar amount awarded. Sometimes, states incorporate a formula that is then adjusted based on earnings and financial situation of each spouse.
Additional dollars for support may be granted for extras such as summer camp, college, life insurance for the paying parent, private school, and even for extensions beyond the age of eighteen. They are normally incorporated into separation agreements since they are beyond what the law requires. The court can enforce the extra support if the separation agreement has been signed by both parents.
If and when any changes occur, such as living arrangements of the child(s), then those changes need to be documented and given to the court. Child support payments can be affected since a non-custodial parent who becomes a custodial parent should not then have to pay alimony and support to a parent that is not “taking care” of the child(s).