Most states have child support guidelines in their statutes—often in the statutes collected in the state’s family code. These child support guidelines provide percentages and methods of calculating child support payments based on the number of children; the parents’ incomes and financial resources; the income and needs of the custodial parent; the needs of the children, including any special needs; and the standard of living for the children before the parents’ divorce or separation. The child support guidelines are just guidelines, and the court generally has discretion to order more or less child support based on the best interest of the children.

In Illinois, child support guidelines are established by state law to ensure that children receive adequate financial support from their parents following a divorce or separation. These guidelines are found in the Illinois Marriage and Dissolution of Marriage Act. The amount of child support is calculated using an 'income shares' model, which considers the combined income of both parents and the number of children to be supported. The guidelines provide tables that specify the percentage of the combined parental income that should be allocated for child support based on the number of children. Additionally, the court will consider other factors such as the financial resources and needs of both parents, the standard of living the children would have enjoyed had the marriage not been dissolved, and the physical and emotional condition of the children, including any special needs they may have. While the guidelines serve as a standard calculation method, Illinois courts have the discretion to deviate from these guidelines if it is determined to be in the best interest of the children. Such deviations must be justified in writing by the court.