Illinois Child Support Calculator and
Guidelines Worksheet

Illinois calculates child support under the Income Shares model, effective July 1, 2017, codified in 750 ILCS 5/505. Before July 2017, Illinois used a simpler Percentage of Income model — the switch to Income Shares significantly changed how courts determine support in cases where the recipient parent earns meaningful income.

The current approach combines both parents' net income and divides the total obligation proportionally.

Illinois's calculation starts with each parent's net income — gross income minus federal and state income taxes, Social Security and Medicare taxes, mandatory retirement contributions, union dues, prior child support obligations, and health insurance premiums for the child. Combined net income is matched against the Illinois Schedule of Basic Obligations, and each parent's share of the obligation is proportional to their percentage of combined net income.

The Illinois Department of Healthcare and Family Services Division of Child Support Services administers statewide enforcement.

Illinois adds work-related childcare and health insurance to the base obligation, allocated proportionally by net income. Courts may deviate from guidelines when applying the standard amount would be inappropriate — common deviation factors include the financial resources and needs of the child, the standard of living the child would have enjoyed, physical and emotional conditions of the child, and educational needs.

Illinois courts can also order support for educational expenses beyond age 18 under 750 ILCS 5/513 in appropriate cases.

Use this illinois child support calculator to estimate your child support obligation before consulting a family law attorney. The Illinois Schedule of Basic Obligations includes a conversion chart to move between weekly, bi-weekly, and monthly income figures.

Illinois state guidelines also reference federal poverty guidelines when calculating the self-support reserve — a minimum income floor that protects the paying parent from being reduced below subsistence. For shared parenting arrangements, Illinois applies a shared parenting adjustment when both parents have significant overnights.

Spousal maintenance (alimony) paid by the obligor parent is deducted before calculating net income, which can affect actual child support for one child or multiple children. Parents can estimate their child support obligation with this calculator, then verify the result with a family law attorney familiar with Illinois state guidelines.

Under Illinois's Income Shares model, the calculation begins by determining each parent's gross income from all sources, including wages, salaries, commissions, bonuses, self-employment income, rental income, and certain benefits. The court then applies allowable deductions — such as taxes, mandatory retirement contributions, and pre-existing child support obligations — to arrive at each parent's adjusted or net income.

Both incomes are combined to find the total household income available for child support.

The combined income figure is then matched against Illinois's child support schedule (referenced in Income Shares model using both parents' combined net income with the Illinois Schedule of Basic Support Obligations), which provides a base obligation amount for the number of children involved. For example, under a typical Income Shares schedule, parents with a combined monthly income of $8,000 and two children have a presumptive obligation of $1,400 per month.

Each parent's share is then calculated in proportion to their contribution to the combined income — if one parent earns 60% of the total, they are responsible for 60% of the base obligation.

Additional expenses are layered on top of the base obligation. Health insurance premiums for the child, work-related childcare costs, and extraordinary expenses (such as special education or medical needs) are typically added to the base figure and divided proportionally between the parents.

The custodial parent's share is assumed to be spent directly on the child, while the non-custodial parent's share becomes the child support payment.

The number of children is the most direct factor in any Illinois child support calculation under the child support guidelines in Income Shares model using both parents' combined net income with the Illinois Schedule of Basic Support Obligations. The basic child support obligation increases with each additional child, though not in a strictly linear fashion.

The amount of child support also depends on each parent's monthly gross income, which includes wages, salary, commissions, bonuses, and other recurring sources. The noncustodial parent's share is calculated based on their proportion of the combined monthly gross income.

Health care and child care costs play a major role. The parent who carries the child's health insurance receives a credit or offset, and unreimbursed medical expenses exceeding a threshold are typically split between the parents.

Child care costs necessary for employment or education are added to the basic child support obligation and divided proportionally between parents.

Children with special needs — whether physical, developmental, or educational — can significantly increase the amount of child support. Illinois courts operating under 750 ILCS 5/505 have discretion to deviate upward from the guideline amount when a child requires therapies, specialized schooling, or ongoing medical treatment that exceeds ordinary expenses.

Similarly, extracurricular activities and private school tuition may be considered, though courts vary in how they treat these costs.

High-income cases present unique challenges. Where Illinois's schedule under Income Shares model using both parents' combined net income with the Illinois Schedule of Basic Support Obligations sets a maximum combined income threshold, courts exercise independent discretion above that cap rather than applying the standard table.

When a parent is voluntarily unemployed or underemployed, Illinois courts may impute income — assigning an earning capacity based on the parent's education, work history, job market conditions, and prior earnings — to prevent artificially lowering the child support amount by choosing not to work or accepting a lower-paying job without justification.

Illinois's child support obligation generally continues until the child reaches the age of majority under state law — check 750 ILCS 5/505 for the specific cutoff age, which may extend beyond 18 in certain circumstances such as a child still in high school or college. Support may also end earlier if the child becomes emancipated through marriage, military service, or court order.

Either parent may petition the court under 750 ILCS 5/505 to modify a child support order when there has been a material change in circumstances. Common triggers include:

• A significant income change for either parent (a material change in circumstances — such as a significant income shift, change in custody arrangement, or change in the child's needs — is generally required to modify the existing order; the exact threshold under 750 ILCS 5/505 controls for Illinois)
• Loss of employment or onset of a disability
• A significant change in the child's medical, educational, or developmental needs
• A substantial change in the custody or parenting-time arrangement

The parent seeking modification bears the burden of proving that circumstances have genuinely changed since the last order.

Modifications in Illinois under 750 ILCS 5/505 are not automatic — even when circumstances change, the existing order remains in effect until a court enters a new one. Filing promptly matters because modifications typically take effect from the date of the petition, not retroactively to when the change occurred.

Parents who delay filing risk accumulating arrears under the original order that cannot be forgiven, since federal law prohibits retroactive reduction of child support arrears. Families navigating this process should contact a Illinois family law attorney to confirm the specific modification threshold and filing procedures that apply to their order.

Illinois has multiple enforcement mechanisms under 750 ILCS 5/505 to ensure child support is paid. The most common tool is income withholding (wage garnishment), which is now mandatory for most new and modified child support orders.

Under an income withholding order, the obligor's employer deducts the support amount directly from their paycheck and sends it to the state disbursement unit. This approach removes the obligation from the paying parent's discretion and provides the custodial parent with reliable, timely payments.

When wage garnishment is insufficient or the obligor is self-employed, Illinois can pursue additional enforcement actions:

• Intercepting federal and state tax refunds
• Placing liens on real and personal property
• Suspending driver's licenses and professional or occupational licenses
• Denying or revoking passport applications for arrears exceeding $2,500
• Reporting delinquent obligors to credit bureaus

Each tool creates significant practical consequences that apply without a separate court hearing.

In severe cases, Illinois courts may hold a non-paying parent in contempt of court, which can result in fines, community service, or incarceration. Repeated willful failure to pay can lead to criminal prosecution under both state and federal law.

The Deadbeat Parents Punishment Act makes it a federal crime to willfully fail to pay child support for a child living in another state when the arrearage exceeds $5,000 or has been unpaid for more than one year. The federal Office of Child Support Services (OCSE) can assist custodial parents with enforcement at no cost.

To contact the Illinois child support program directly, use the OCSE state programs directory.

The amount of parenting time each parent exercises directly affects the child support calculation in Illinois. When the non-custodial parent has the child for a significant number of overnights — typically 25% or more of the year (approximately 92 overnights in many jurisdictions) — Illinois's guidelines under Income Shares model using both parents' combined net income with the Illinois Schedule of Basic Support Obligations apply a shared-custody or parenting-time adjustment that reduces the non-custodial parent's obligation.

A parent who has the child more often incurs more direct expenses for housing, food, and daily needs, so the transfer payment to the other parent reflects that shared financial responsibility.

In cases where parents share custody equally (50/50), Illinois courts typically still calculate support based on the income differential between the parents. The higher-earning parent generally pays support to the lower-earning parent, even in a true 50/50 arrangement, because the child's standard of living should be roughly comparable in both households.

The amount is usually significantly lower than in a traditional custody arrangement as calculated under Income Shares model using both parents' combined net income with the Illinois Schedule of Basic Support Obligations. Even small changes in the overnight count — such as moving from 120 to 128 overnights — can cross a threshold that triggers a meaningful change in the support calculation.

Use the Illinois Custody Time Calculator to track overnights precisely and determine which parenting time threshold applies to your schedule.