A Big Change is Coming to Child Support Calculations

By Rachael Toft

Since 1984, child support in Illinois has been calculated solely on the non-residential parent’s net income.[1] The income of the residential parent was not considered and a flat percentage was applied to the non-residential parent based on the number of children. In contrast, the new law (the “income shares” model) considers both parents’ income in calculating child support, such that each parent is responsible for his or her own prorated share of the basic child support obligation.

The new law will take effect July 1, 2017 for all child support calculations. Illinois will join 39 other States that have already enacted an income shares model.[2] An income shares model attempts to consider a family’s actual child rearing expenses and more accurately allocate responsibility for those costs between the parents.[3] Public Act 99-764 (Illinois House Bill 3982) amends sections 505 and 510 of the Illinois Marriage and Dissolution of Marriage Act (“IMDMA”) for calculating child support. [4]

The Income Shares Calculation

The first step is to calculate the net income for each parent. The definition of income will continue to be all income from all sources, although a few exemptions were included such as, TANF, SNAP or SSI.[5] Unlike the current child support law, the new law includes a provision for imputing income to a voluntarily unemployed or underemployed parent.[6]

The second step is to compare the combined net income of the family to a schedule that provides the basic child support obligation. The schedule is based on estimates for child rearing costs for an average intact family with similar income and number of children. The schedule will be published by the Illinois Department of Healthcare and Family Services (“HFS”).[7]

The third step is to allocate child rearing costs to each parent. The allocation is based on each parent’s percentage share of the total net income.

The basic child support obligation does not include extracurricular activities, child care expenses, health or medical coverage or health care needs not covered by insurance. The court may order either or both parents to contribute to those additional expenses on top of basic support.[8] These additional expenses will typically be totaled and then proportionately shared between the parents based on their respective percentage of income.

Shared Parenting Time and the Shared Care Child Support Obligation

Currently, child support is paid by the non-residential parent to the residential parent, regardless of the amount of time a non-residential parent may spend with the child. The new law addresses the situation where a “non-residential” parent has significant parenting time. Specifically, the new law establishes a threshold shared parenting time such that when a child spends 40% of the time with a parent (at least 146 overnights a year), then the “non-residential” parent’s support obligation may be reduced.[9]

Existing Support Orders

The new law going into effect does not automatically change the terms of an existing child support order. Nor does the enactment of the new child support law constitute a “substantial change in circumstances” for purposes of modifying a previously established support order.[10] Pending cases that will be heard after July 1, 2017 will be calculated pursuant to the new guidelines.


The income shares model seeks to better serve the financial support needs of a child and create flexibility for shared parenting schedules.

Rachael Toft focuses her practice on family law and adoption. She founder of Law Offices of Rachael Toft,

[1] 750 ILCS 45/et al. now since repealed. Illinois Parentage Act of 2015 750 ILCS 46/et al, effective January 1, 2016 replaced.

[2] For more detail on State by State comparison, see the  National Conference of State Legislatures at

[3] 750 ILCS 5/505(a)(1)

[4] Public Act 99-764 signed into law August 12, 2016 at

[5] 750 ILCS 5/505(a)(3)(A)

[6] 750 ILCS 5/505(a)(3.2)

[7] The current income share schedule was released by HFS in April but is still marked as draft. However, as July 1st is quickly approaching, this chart will likely become the final model.

[8] 750 ILCS 5/505(a)(3.6), (3.7), & (4)

[9] 750 ILCS 5/505(a)(3.8)

[10] 750 ILCS 5/510(a)