Illinois Child Support Calculator
Estimate using the statutory shared physical care formula (146+ overnights each), 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)
The 146 Night Rule (through December 31, 2026): If each parent has the children for at least 146 overnights per year, the statutory "shared physical care" formula applies, which often — but not always — reduces the support obligation depending on the parents' relative incomes and overnight counts. Beginning January 1, 2027, the threshold drops to 110 overnights; this calculator switches automatically. What changes January 1, and who it 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.