Illinois uses the Income shares and measures income as net income. Illinois converts incomes to net, combines them, and applies income-shares schedules with parenting-time adjustments. Shared physical care and add-ons for health insurance and childcare are handled on standardized worksheets. That is what separates Illinois how child support is calculated from a generic national summary. Read 750 ILCS 5/505 before the background sections below. Support generally ends when Support generally continues until age 18, or 19 if still in high school; contribution to post-secondary expenses may be ordered separately. Modification: Substantial change in circumstances; income or parenting-time changes commonly reopen the worksheet.
How child support is calculated in Illinois
- Identify each parent's guideline income using net income as defined in 750 ILCS 5/505 and the accompanying worksheets or administrative rules.
- Apply the income shares — whether that means a combined-income schedule, an obligor percentage table, or a Melson-style self-support reserve plus primary obligation.
- Allocate add-ons such as health insurance premiums, unreimbursed medical expenses, and work-related child care according to Illinois practice.
- Consider parenting time adjustments where the guidelines or case law authorize a credit or shared-custody formula.
- Test for deviation if a strict guideline result would be unjust or inappropriate on the record.
Online calculators can illustrate ranges, but only the controlling statute, guidelines, and court findings produce an enforceable order.
Deviation from the guidelines
Courts may deviate for extraordinary medical needs, educational expenses, shared care complexities, and other § 505 factors when the guideline is inequitable.
When a court departs from the presumptive amount, Illinois practice generally requires findings that explain why the guideline figure is unjust or inappropriate and what amount better serves the child's needs. Those findings matter on appeal and in later modification proceedings.
Modification of child support
Substantial change in circumstances; income or parenting-time changes commonly reopen the worksheet.
A parent seeking a change typically must show that circumstances after the prior order make the existing award inequitable. Common triggers include job loss, substantial income changes, a new parenting-time schedule, emancipation of a child, or extraordinary medical needs. Retroactivity and temporary relief rules are statute-specific — check 750 ILCS 5/505 and local family-division procedures.
A concrete Illinois scenario
Here is one way the Illinois pieces fit together. Change any fact and the statute may point somewhere else.
Two parents in Illinois need a presumptive child-support figure and may have facts that justify a departure.
- Measure guideline income as net income under 750 ILCS 5/505.
- Apply the Income shares: Illinois converts incomes to net, combines them, and applies income-shares schedules with parenting-time adjustments. Shared physical care and add-ons for health insurance and childcare are handled on standardized worksheets.
- Test deviation: Courts may deviate for extraordinary medical needs, educational expenses, shared care complexities, and other § 505 factors when the guideline is inequitable.
- If circumstances later change: Substantial change in circumstances; income or parenting-time changes commonly reopen the worksheet.
The enforceable number is the Illinois guideline result under 750 ILCS 5/505, plus any deviation findings. HFS Division of Child Support Services uses income withholding, intercepts, contempt, and license remedies.
Enforcement in Illinois
HFS Division of Child Support Services uses income withholding, intercepts, contempt, and license remedies.
Interstate cases often implicate UIFSA. Income withholding, contempt, license suspension, and tax-refund intercept remain core tools nationwide, but the Illinois child support agency and clerk of court procedures control day-to-day collection.
When child support ends
In Illinois, Support generally continues until age 18, or 19 if still in high school; contribution to post-secondary expenses may be ordered separately. Orders may extend for disability, secondary education, or other statutory grounds where the statute allows. Always read the judgment language — agreed orders sometimes set a different end date or require a notice of emancipation.
Case law: how Illinois courts apply the guidelines
The opinions below are in the LawDiver corpus. Each block quote is taken from the opinion text so you can jump from this guide into the full decision.
In re Marriage of McGrath
In re Marriage of McGrath, 2012 IL 112792 (2012)
…stitutes no part of considered his “income” for purposes of child support; but, on remand, the opinion of the court if the court finds that an appropriate support amount cannot be generated but has been prepared by following statutory guidelines, it should so state, explain its reasons by the Reporter of for deviating therefrom, and make an adjusted award. Decisions for the con…
On child support, In re Marriage of McGrath speaks to the Illinois dispute in this passage: "Reporter of for deviating therefrom, and make an adjusted award." The surrounding opinion shows how the court applied that language to the record.
In re Marriage of Sobieski
In re Marriage of Sobieski, 984 N.E.2d 163 (2013)
…orney fees and $4,800 each month for constitutes no part of child support was affirmed on the grounds that the trial court gave the opinion of the court consideration to the statutory factors relevant to the contribution to but has been prepared petitioner’s attorney fees and the statutory guidelines were followed with by the Reporter of regard to child support. Decisions for t…
On child support, In re Marriage of Sobieski speaks to the Illinois dispute in this passage: "orney fees and $4,800 each month for constitutes no part of child support was affirmed on the grounds that the trial court gave the opinion of the court consideration to the statutory factors relevant to the contribution to but has been prepared petitioner’s attorney fees and the" The surrounding opinion shows how the court applied that language to the record.
In re Marriage of Salvatore
In re Marriage of Salvatore, 2019 IL App (2d) 180425 (2019)
…Salvatore, appeals the denial of his petition to modify his child support obligation. He argues that the McHenry County circuit court’s ruling was erroneous because there has been a substantial change in circumstances since the dissolution of his marriage to petitioner, Brenda Salvatore. Namely, Daniel argues that his child support obligation should be decreased based on Brenda…
In re Marriage of Salvatore is worth reading on Illinois child support because the court put the point in its own words: "Salvatore, appeals the denial of his petition to modify his child support obligation." Use that passage as the starting point, then read the facts that precede it.
In re Marriage of Turk
In re Marriage of Turk, 2014 IL 116730 (2014)
…6730 Filed June 19, 2014 Held Statutory guidelines permit a child support award to a noncustodial (Note: This syllabus parent where warranted by circumstances and the best interests of the constitutes no part of the child, such as where visitation expenses were incurred by a poorer but opinion of the court but noncustodial parent. has been prepared by the Reporter of Decisions…
Practitioners open In re Marriage of Turk when Illinois child support turns on the distinction in this sentence: "Note: This syllabus parent where warranted by circumstances and the best interests of the constitutes no part of the child, such as where visitation expenses were incurred by a poorer but opinion of the court but noncustodial parent." Do not lift it out of the facts the court was deciding.
In re Marriage of Connelly
In re Marriage of Connelly, 145 N.E.3d 724 (2020)
…rties’ two children to Stacy and required Ryan to pay Stacy child support. Less than a year later, Ryan filed a petition to increase his parenting time, which the trial court granted. One year later, Ryan filed a petition to modify child support. Following a hearing, the trial court denied Ryan’s petition. Ryan appeals, arguing that the trial court’s denial of his petition cons…
Illinois opinions such as In re Marriage of Connelly are cited where child support is disputed. The court stated: "Stacy and required Ryan to pay Stacy child support. Less than a year later, Ryan filed a petition to increase his parenting time, which the trial court granted. One year later, Ryan filed a petition to modify child support." That is the language to brief; the rest of the decision supplies the procedural posture.
In RE MARRIAGE OF McGRATH
In RE MARRIAGE OF McGRATH, 361 Ill. Dec. 12 (2012)
…y be included in the calculation of net income when setting child support under section 505 of the Illinois Marriage and Dissolution of Marriage Act (the Act) (750 ILCS 5/505 (West 2010)). We hold that it may not. ¶ 2 BACKGROUND ¶ 3 On September 14, 2007, the circuit court of Cook County entered a judgment dissolving the marriage of petitioner Mary Ellen McGrath and respondent…
Practitioners open In RE MARRIAGE OF McGRATH when Illinois child support turns on the distinction in this sentence: "Illinois Marriage and Dissolution of Marriage Act (the Act) (750 ILCS 5/505 (West 2010)). We hold that it may not." Do not lift it out of the facts the court was deciding.
In re Marriage of McGrath
In re Marriage of McGrath, 2011 IL App (1st) 102119 (2011)
…0–2119 Filed June 30, 2011 Held In determining respondent’s child support obligation, the trial court (Note: This syllabus properly found that respondent's withdrawals from his savings accounts constitutes no part of the constituted income, since the Illinois Marriage and Dissolution of opinion of the court but Marriage Act defines “net income” as “the total of all income from…
Illinois opinions such as In re Marriage of McGrath are cited where child support is disputed. The court stated: "0–2119 Filed June 30, 2011 Held In determining respondent’s child support obligation, the trial court (Note: This syllabus properly found that respondent's withdrawals from his savings accounts constitutes no part of the constituted income, since the Illinois Marriage and Dissolu" That is the language to brief; the rest of the decision supplies the procedural posture.
In re Marriage of Rice
In re Marriage of Rice, 2011 IL App (1st) 103753 (2011)
…proceedings, the trial court’s modification of respondent’s child support constitutes no part of obligation by setting a lump-sum obligation rendered inapplicable the the opinion of the court reduction provision of the parties’ marital settlement agreement reducing but has been prepared respondent’s obligation by 24% as each child became emancipated and by the Reporter of his s…
On child support, In re Marriage of Rice speaks to the Illinois dispute in this passage: "proceedings, the trial court’s modification of respondent’s child support constitutes no part of obligation by setting a lump-sum obligation rendered inapplicable the the opinion of the court reduction provision of the parties’ marital settlement agreement reducing but has been p" The surrounding opinion shows how the court applied that language to the record.
Practical checklist for Illinois child support matters
- Gather recent pay stubs, tax returns, and proof of health insurance / child-care costs.
- Complete the current Illinois worksheet or financial affidavit required by the local court.
- Document parenting-time overnights if a shared-custody adjustment may apply.
- Flag facts that could support deviation (special needs, travel costs, high income, other children).
- Search LawDiver for recent Illinois appellate decisions before mediation or trial.
Key takeaways
- Illinois follows the Income shares model for presumptive child support.
- Income is generally measured using net income, then allocated under 750 ILCS 5/505.
- Guideline amounts are presumptive, not automatic — courts may deviate when the facts justify it.
- Support generally continues until age 18, or 19 if still in high school; contribution to post-secondary expenses may be ordered separately.
- Either parent can seek modification when substantial change in circumstances; income or parenting-time changes commonly reopen the worksheet..
- Read the companion guide: Illinois alimony / maintenance.
Statutory framework and guideline model
Illinois's child support system is built around 750 ILCS 5/505. Under the income shares, Illinois converts incomes to net, combines them, and applies income-shares schedules with parenting-time adjustments. Shared physical care and add-ons for health insurance and childcare are handled on standardized worksheets.
Federal law requires every state to maintain presumptive guidelines and to review them at least every four years (42 U.S.C. § 667). Confirm the latest Illinois schedule or worksheet before relying on any online calculator.
Frequently asked questions
How is child support calculated in Illinois?
Illinois uses the income shares under 750 ILCS 5/505. Courts start with net income, apply the guideline schedule or percentage, allocate add-ons, and may deviate with findings when the presumptive amount is unjust.
What income counts for Illinois child support?
Guideline income generally tracks net income as defined by 750 ILCS 5/505 and the worksheets. Wages, self-employment income, bonuses, and certain benefits are commonly included; exact deductions and exclusions are statute-specific.
Can Illinois courts order more or less than the guideline amount?
Yes. Guideline support is presumptive. Judges may deviate when the record shows the guideline result is unjust or inappropriate, typically with written findings explaining the departure.
How do I modify a Illinois child support order?
Substantial change in circumstances; income or parenting-time changes commonly reopen the worksheet. File in the court with continuing jurisdiction (or follow UIFSA for interstate cases) and support the request with current financial evidence.
When does child support end in Illinois?
Support generally continues until age 18, or 19 if still in high school; contribution to post-secondary expenses may be ordered separately. Confirm any disability, educational, or agreed extensions in your particular order.
Where can I research Illinois child support case law?
Use LawDiver search scoped to Illinois, or open the opinions linked in this guide. Companion reading: Illinois maintenance guide.
Disclaimer
This guide is general legal information about Illinois child support, not legal advice. Statutes, guidelines, and case law change. Confirm the current text of 750 ILCS 5/505 and consult a licensed Illinois family-law attorney about your facts.