Illinois Child Support Calculator (2026)

How Illinois calculates child support

Illinois replaced its old percentage-of-income model with an income-shares model in 2017. The current rule is in 750 ILCS 5/505. The basic obligation comes from a schedule that pairs combined monthly net income with the number of children. The 2026 schedule took effect on March 20, 2026, and runs from $25 to $27,374.99 of combined net income in $50 brackets.

Once the basic obligation is known, each parent receives a percentage share based on their net income. The parent who pays support owes their share of the basic obligation. The other parent’s share is treated as the contribution they make by caring for the child directly. Add-ons and shared-parenting adjustments are applied after the basic obligation, not before.

The schedule is not a flat percentage. The amount rises with income but at a declining rate, which is why the table is used instead of a single multiplier. A family with $8,000 of combined net income and one child has a different basic obligation than a family with $16,000, and the difference is not exactly double.

Net income and the 2026 schedule

Net income starts with gross income from employment, self-employment, bonuses, commissions, overtime, and other recurring sources. Illinois then subtracts federal and state income taxes, Social Security and Medicare, mandatory retirement contributions, union dues, health insurance premiums, and prior court-ordered support. The goal is to measure the income available for the child, not the amount before withholding.

The form takes net income. Using gross salary instead of net income would push the estimate too high. For a self-employed parent, the deduction analysis can be more complex, and the court may adjust for ordinary and necessary business expenses. If the parents disagree about income, the official HFS calculator or an attorney is the better next step.

The 2026 schedule is published as a PDF by the Illinois Department of Healthcare and Family Services. The calculator uses the bracket that contains the combined income. The schedule does not interpolate between rows; the row for the bracket applies.

Shared parenting and the 146-night rule

Illinois uses a different calculation when each parent has at least 146 overnights per year. That is the threshold for “shared parenting” under the statute. The shared-parenting calculation accounts for the time the child spends with each parent and can reduce or change the transfer compared with a primary-custody calculation.

The calculator covers basic support for a primary custodial schedule. It does not apply the shared-parenting adjustment, the 146-night analysis, or the split-care rules for children who live with different parents. If you have shared parenting, use the official HFS calculator or a lawyer; a basic estimate can be materially wrong in that situation.

Add-ons and maintenance

Basic support does not include work-related childcare, the children’s health insurance premium, extracurricular activities, or uninsured medical expenses. Illinois generally allocates those add-ons between the parents in proportion to income, but the court can order a different split. The calculator does not add them.

Maintenance is also outside the estimate. Maintenance paid under a court order can reduce the paying parent’s net income, and maintenance received can increase the recipient’s net income. The tax treatment depends on the date of the order and the federal rules that applied when it was entered. If maintenance is part of your case, the child support worksheet needs to show it.

An Illinois example at $8,000 combined net

For a household with Parent A at $5,000 and Parent B at $3,000 in monthly net income, combined income is $8,000. The 2026 schedule gives a basic obligation of $1,444. That leaves Parent A with a 62.5% share: $903 per month.

If the same parents have two children, the schedule amount is higher and Parent A’s share is applied to that larger obligation. Shared parenting, add-ons, or maintenance would change the result; this is a basic guideline figure, not the court’s order.

What the Illinois estimate leaves out

• The 146-night shared-parenting adjustment.
• Split care for children who live with different parents.
• Work-related childcare and after-school care.
• The children’s health insurance premium and uninsured medical costs.
• Extracurricular activities and school expenses.
• Maintenance paid or received.
• Deviations for special needs, extraordinary expenses, or other factors the statute allows.
• Unpaid arrears, interest, and credits for benefits paid on the child’s behalf.

The result is only as reliable as the net income you enter. A self-employed parent, or one with irregular income, may have income adjusted before the schedule is applied; voluntary underemployment can also lead to imputed income. That adjustment can change the result more than the schedule itself.

When Illinois’s official calculator is the better choice

The Illinois HFS Income Shares Calculator is the official tool. It handles the net-income conversion, the shared-parenting adjustment, maintenance, and add-ons, and it produces a worksheet that can be filed. Use it if you need a filing-ready calculation or if the case involves shared parenting.

A family law attorney is the right next step if the parents disagree about overnights, income, or maintenance. The 2026 schedule is a guideline, and the court can deviate when the facts justify it. The calculator helps you see the structure of the number, not the final order.

Frequently asked questions