Federal law requires each state to adopt some form of child support guidelines. Courts in each state are required to follow the guidelines in establishing child support obligations.

Each state has adopted child support guidelines that determine the method of calculating a parent's child support obligation. There are three main types of guidelines used by the states. The first is the flat percentage model. Under the flat percentage model, the state determines the percentage of each person's income that should be used for the support of the child. The percentage increases as the number of children increase and in some states as the income increases. To this base amount, there may be adjustments based on the circumstances of the child and the parents. The second type of guideline, called the Income Share model, is a chart that allocates the amount that should be used to support the child or children of the parties based on the total combined income of the parties and the number of children. To this also adjustments are made for circumstances such as responsibility for other children or extraordinary medical expenses. The third model is based on guidelines developed by the State of Delaware. Under that model, the court computes the income of the parent, subtracts from it an amount the parent needs for his or her own support, and then determines the available net income for child support. Where the parent's income is too low to meet his own support needs, the court will still set some amount for child support.

Basic child support is supposed to cover the basic needs of a child at a standard based on the income of the parents. Basic support includes such expenses as housing, food, clothing, school supplies, transportation, spending money, school and after-school activities, hair cuts, and all the other everyday expenses of raising a child. In calculating child support in all three models, some adjustments as to income or expenses are considered. The court must consider any alimony either parent is required to pay or may receive and responsibility to provide for other children. Expenses considered by the court include day care expenses for the young child of a working parent, any health insurance provided for the child, and extraordinary medical expenses. A court may also consider excessive travel expenses where the parents live far apart. In addition, the court may allocate the cost of private or parochial school as part of child support, where the child has always attended such school or the parents agree to provide such education.

State courts and child support enforcement agencies are required to follow the child support formula adopted by the state in calculating child support unless the court finds a good reason for deviating and puts that reason in writing at the time child support is ordered. Where a child has additional income from a source other than the mother and father, such as a trust fund or a Social Security benefit based on the earnings of a stepparent, the court may, but is not required, to deviate from the guidelines. The court may also deviate where a parent, under state law, is required to contribute toward the support of the parent's mother or father or has done so over the course of the marriage.