New Child Support Law

Illinois joined a majority of other states in adoption the new "income shares model" for child support calculation method. This took effect on July 1, and replaces the previously-used "percentage of income" that many parents may be familiar with. This occurred with the enacting of Public Act 99-764, which completely changed the child support guidelines of Illinois Marriage and Dissolution of Marriage Act

The new income shares model is based on real data that takes factors into account other than just the income of one parent. It calculates child support using actual child-rearing costs that are based in part on data from the Bureau of Labor Statistics. The Illinois Department of Health and Family Services uses that data to publish its Schedule of Basic Child Support Obligation (the Schedule) (

So, how does it work? 

The new computation is based on several factors. First, the net monthly income for each parent is determined. Income from all sources is included in the calculation. This means that if a party is receiving spousal maintenance, either from the divorcing spouse or a prior relationship, that amount is factored into net income. A party that pays maintenance from a prior relationship has that amount deducted from their net income. However, government benefits like Temporary Assistance for Needy Families, the Supplemental Nutritional Assistance Program, and SSI are not included as income.

Parties can choose to use either of two different tax-based formulas to determine net income: a simplified standardized tax amount formula or an individualized tax amount formula. The standardized formula treats both parties as individual filers who claim one dependency exemption. A gross-to-net-income conversion chart can be found here: The individualized formula considers the actual filing status of the parties, their dependency allocations, and tax credits.

The parents, on their own or with attorneys, can also agree to another amount if the Court (judge) approves and does not find it unconscionable.  Once the individual net monthly incomes are determined, they are added together. This combined income amount is then matched to its corresponding entry on the Schedule, which is based on the number of children from one to six. For example, if a divorcing couple has a combined adjusted monthly net income of $10,000 and only one child together, their basic support obligation for that child is $1,445 per month.

Once the basic support obligation is determined, the percentage contributions of each parent's income is determined. It is a simple calculation. The individual's monthly net income is divided by the combined monthly net income. Returning to our example, if the parties' combined monthly net income is $10,000 with one parent earning $2,500 and the other $7,500, their percentage contributions would be 25 and 75 percent, respectively.

The parent who has the majority of parenting time receives the support payment, which is calculated by multiplying the basic support obligation by the payor's income share. It is presumed that the payee will use their own percentage contribution to care for the child. In our example, if the parent earning $2,500 per month has the majority of parenting time, then he or she will receive $1,083.75 per month in child support (the other parent's 75% contribution multiplied by the $1,445 basic support obligation). That same parent will be presumed to spend his or her own percentage contribution to care for the child (i.e., $361.25 per month, which is 25 percent of the $1,445 basic support obligation). Bennett says that this increases the perception of fairness and equity in child support. Both parents' contributions to the support obligation are acknowledged.

Shared-parenting adjustment

Other factors can adjust the support obligation. If it turns out that either / both parents have 146 or more parenting overnights a year, the shared parenting adjustment kicks in. The shared parenting adjustment is a two-step calculation. First, the basic support obligation is multiplied by 1.5. This accounts for the increased child-rearing costs for both parents in a shared parenting situation. The parents' contributions are then determined. Those amounts are adjusted by the percentage of parenting time allocated to the other parent.