Illinois Child Support Calculator
Estimation using the "Shared Care" (146 Overnights) logic and HFS Gross-to-Net conversion tables.
1. Financial Inputs
2. Parenting Time (Overnights)
The 146 Night Rule: 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.
Estimated Monthly Obligation
Paid by Parent A
*Estimates based on HFS 2025 Schedule.
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 Critical "146 Night" Cliff
One of the most consequential numbers in Illinois child support is 146. This is the threshold for "Shared Physical Care."
- Under 146 Nights: The parent with the majority of time receives the full basic support amount (prorated by income).
- 146 Nights or More: 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.