Illinois Official Form 113 (expandable and calculating) is an official form developed by the Illinois Supreme Court used to calculate the amount of child support owed in the state of Illinois. This form can be used by individuals filing for child support or by court personnel calculating the amount of child support a parent must pay. It is an expandable form that adjusts the amount of child support owed based on the income of the parents, their number of children, and other factors, such as the amount of time each parent spends with the children. There are three types of Illinois Official Form 113 (expandable and calculating): Form 113Â N, Form 113R, and Form 113A. Form113INNN is used to determine the amount of child support owed by a non-custodial parent; Form 113R is used to calculate the amount of child support owed when both parents are receiving public assistance; and Form 113A is used to determine the amount of child support owed when both parents are receiving income other than public assistance.