Illinois calculates child support under 750 ILCS 5/505, an income-shares model that starts by converting each parent’s gross income to net income using the Healthcare and Family Services standardized tables, most recently updated effective March 20, 2026. Parents who each have the children more than 146 overnights per year fall under Illinois’s shared physical care rules rather than the standard formula.
Key facts
| Model | Income shares — 750 ILCS 5/505 |
|---|---|
| Gross-to-net conversion | HFS standardized tables (eff. 2026-03-20) |
| Shared physical care threshold | 146 overnights/year per parent |
Official source: https://www.ilga.gov/documents/legislation/ilcs/documents/075000050k505.htm
Custody arrangements covered
- Standard custody
- Shared physical care (each parent >146 overnights/year)
Frequently asked questions
What statute governs Illinois child support?
750 ILCS 5/505, which uses an income-shares model.
How does Illinois convert gross income to net income?
Using the Healthcare and Family Services (HFS) standardized gross-to-net conversion tables, effective March 20, 2026 in the version this calculator uses.
What is Illinois’s shared physical care threshold?
146 overnights per year for each parent — above that, Illinois applies its shared physical care calculation instead of the standard formula.
Is this calculator an official Illinois tool?
No — it’s an independent estimate built on the HFS tables and § 505, not a substitute for the state’s own calculation or legal advice.
Update history
- — Illinois went live under 750 ILCS 5/505, using the HFS standardized gross-to-net conversion and basic obligation schedule (effective 2026-03-20), with the 146-overnight shared physical care adjustment.