Illinois Child Support Calculator
Estimate using the statutory shared physical care formula (110+ overnights each, the rule effective January 1, 2027), with standardized net income from the HFS gross-to-net table and the HFS schedule of basic obligations, both effective March 20, 2026.
1. Financial Inputs
2. Parenting Time (Overnights)
Preview: the 110 Night Rule (effective January 1, 2027). This estimate uses the rule that takes effect January 1, 2027 under Public Act 104-733: if each parent has the children for at least 110 overnights per year, the statutory "shared physical care" formula applies, and the shared-care support obligation of a parent with 110 to 145 overnights is increased by 2% to 10% under the statute's adjustment table before the two parents' obligations are offset. The statute caps the increased amount at what the basic guidelines would require, and that sentence can be read more than one way; this estimate applies the cap before the two amounts are offset, and the official HFS worksheet controls. The new rule applies when support is set or modified under it; it does not change an existing order by itself. Who the change affects
Estimated Monthly Obligation
Paid by Parent B
*HFS Income Shares Schedule and Gross to Net Income Conversion Table, effective March 20, 2026. Uses standardized net income; it does not include individualized net income, maintenance, or support paid for other children. The official HFS worksheet controls.
Understanding the "Income Shares" Model
Since 2017, Illinois has used the "Income Shares" model (750 ILCS 5/505). This philosophy holds that a child should receive the same proportion of parental income that they would have received if the parents lived together.
The Shared Physical Care Threshold
Through December 31, 2026, shared physical care applies when each parent has at least 146 overnights a year. Beginning January 1, 2027, Public Act 104-733 lowers the threshold to 110 overnights and increases the obligation of a parent with 110 to 145 overnights by a statutory adjustment (10% at 110-114 nights, stepping down to 2% at 140-145), capped at what that parent would owe under the basic guidelines. This calculator applies the rule in effect on the day you use it; before January 1, 2027, you can also preview the new rule. The new rule does not change an existing order by itself: see who the January 1, 2027 change affects.
- Below the threshold: The parent with the majority of time receives the full basic support amount (prorated by income).
- At or above the threshold: The basic support obligation is multiplied by 1.5 to account for duplicated household costs. That amount is then allocated between the parents in proportion to their share of combined net income, multiplied by the percentage of overnights the other parent has, and the two resulting figures are offset so that only the higher amount is paid.