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Illinois Statutory Child Support Calculator

Illinois calculates child support under the Income Shares Model pursuant to 750 ILCS 5/505 based on combined net monthly parental incomes. When each parent exercises at least 146 overnights per year (40%), Illinois applies the Shared Physical Care formula under § 505(a)(3.8), multiplying the basic support obligation by 1.5 and cross-allocating by respective overnight percentages. Official statutory authority: 750 ILCS 5/505.

Specialized Scenarios:50/50 Shared Custody ↓High-Income Deviation ↓Sole Custody Guidelines ↓
Statutory Scope: This page calculates estimated Child Support under 750 ILCS 5/505. It does not compute Spousal Support (Alimony). Child support is determined strictly for minor children.

Statutory Case Parameters

Illinois (IL)
1Governing Jurisdiction
Statutory Basis: 750 ILCS 5/505
2Monthly Incomes & Allowable Deductions
$
Pre-tax salary, wages, business revenue
$
Mandatory union dues & retirement
$
Pre-tax salary, wages, business revenue
$
Mandatory union dues & retirement
3Number of Dependent Children Covered
4Annual Custody Overnights (Out of 365)
Parent A: 183 Overnights (50.1%) Parent B: 182 Overnights (49.9%)
0 nights (Sole Parent B)183 nights (Equal 50/50)365 nights (Sole Parent A)
5Children's Health Insurance Premium
$
Only incremental premium for child(ren)
Cost is credited or prorated by income shares
Parent A (Payor)IL Guideline
Estimated Baseline Guideline Amount
$470 / mo
Annualized: $5,640 / year
⚠️ESTIMATE ONLY — NOT LEGAL ADVICE

This automated tool calculates a preliminary statutory guideline estimate. Actual child support orders are determined by a judge and frequently deviate based on health insurance, childcare, taxes, and judicial discretion.

Notice: This tool calculates Child Support, not Spousal Support (Alimony).
Combined Income$12,000
Basic Support Total$3,240
Parent A Share62.5%
Parent B Share37.5%
Independent Legal NoticeIL Family Law Guidance

When to Consult a Licensed Illinois Family Law Attorney

Judges in Illinois routinely depart from statutory guideline math when specific deviation factors exist (unusual travel costs for visitation, private school tuition, extraordinary medical needs, or dual-household expenses).

  • ■Evaluate discretionary deviation thresholds for your specific jurisdiction
  • ■Verify allowable self-employment deductions & net resource offsets
  • ■Draft enforceable formal stipulations with the clerk of court
Find Licensed Counsel via Official Bar Directory →

Alimonify is an independent informational calculation tool and is not a law firm, legal aid provider, or certified lawyer referral service. Alimonify does not provide legal representation, legal advice, or attorney referral services.

Statutory Framework Analysis

Illinois Legal Mechanics & Court Standards

Legislative Formula & Terminology

Combined net monthly incomes determine basic support from the HFS schedule. If overnights reach 146+, basic support is multiplied by 1.5, apportioned by income shares, and cross-multiplied by the percentage of time spent with the other parent.

  • Custodial Parent Term: Parent with Majority Parenting Time
  • Obligor Parent Term: Support Obligor / Non-Majority Parent
  • Shared Custody Regime: Shared Physical Care (≥ 146 Overnights / 40%)
  • Official Court Form: Shared Physical Care Child Support Worksheet (Form HFS 3989)

Key Statutory Thresholds (2025/2026)

Shared Custody Trigger146 Overnights
Triggers cross-credit calculation
Statutory Cap$30,000/mo
$360,000/yr ceiling
Self-Support Reserve$1,050/mo
Protected subsistence income
Minimum Order Floor$40/mo
Statutory floor for indigent payors
Custody & Income Case Law Compendium

Illinois Custody Schedules, High-Income Caps & Precedent

How Illinois family courts apply 750 ILCS 5/505 across 50/50 equal parenting schedules, high-net-worth income deviations, and traditional sole physical custody orders:

Equal Parenting Time

Illinois: 50/50 Shared Custody

Load 50/50 Shared Custody Preset ↑

Statutory Rule: Under 750 ILCS 5/505(a)(3.8), equal 50/50 custody triggers the Shared Physical Care formula, multiplying basic support by 1.5 and prorating by reciprocal overnights.

Key Statutory Rules

  • Under 750 ILCS 5/505(a)(3.8), equal 50/50 physical custody (182.5 or 183 nights) triggers the statutory 1.5x Shared Physical Care Multiplier.
  • Basic support is grossed up by 150% to reflect dual-residence infrastructural maintenance (bedrooms, clothing, school supplies).
  • Each parent’s grossed-up obligation is multiplied by the percentage of time the child spends in the OTHER parent’s physical care.
  • The parent with the higher net support obligation pays the difference between the two obligations.

Judicial Application & Controlling Case Law

Illinois judges require Form HFS 3989 (Shared Physical Care Worksheet) whenever both parents have 146 or more overnights.

Controlling Authority: 750 ILCS 5/505(a)(3.8); In re Marriage of Scafuri, 203 Ill. App. 3d 385 (2d Dist. 1990).

Practical Calculation Benchmark

Parent A earning $6,000 net (60%) and Parent B earning $4,000 net (40%) with 2 children ($2,460 table × 1.5 = $3,690) results in Parent A paying approximately $364/month to Parent B.

Cap Deviation Analysis

Illinois: High-Income Deviation

Load High-Income Deviation Preset ↑

Statutory Rule: 750 ILCS 5/505 statutory schedule applies up to $30,000/month net income, applying percentage additions or judicial lifestyle discretion on excess.

Key Statutory Rules

  • Under 750 ILCS 5/505(a)(3.5), when combined parental net income exceeds $30,000/month, the court determines child support considering the standard of living the child would have enjoyed.
  • Illinois judges use the $30,000 schedule amount as a baseline ($4,935 for 2 children) and add supplemental discretionary percentages or expenses.
  • Direct payments of private school tuition, travel, and specialized enrichment are prioritized over lump-sum cash transfers.
  • High earners must disclose full financial records, tax returns, and business entity distributions.

Judicial Application & Controlling Case Law

Illinois courts evaluate the child’s historical standard of living and actual proven budgetary needs rather than mechanically extrapolating percentages into millions.

Controlling Authority: In re Marriage of Scafuri, 203 Ill. App. 3d 385 (2d Dist. 1990); In re Marriage of Singleteary, 293 Ill. App. 3d 25 (1st Dist. 1997).

Practical Calculation Benchmark

On combined net income of $45,000/mo for 2 children, court orders baseline $4,935/mo plus 100% direct payment of $3,500/mo private school and tutoring.

Primary Custodian Baseline

Illinois: Sole Custody Guidelines

Load Sole Custody Guidelines Preset ↑

Statutory Rule: Standard Illinois Form HFS 3988 applies when non-majority parent has under 146 overnights, calculating straight pro-rata income share support.

Key Statutory Rules

  • In traditional sole custody arrangements where one parent has primary care (more than 219 overnights / 60%), Form HFS 3988 governs.
  • The non-majority parent pays their straight pro-rata income percentage of the schedule obligation with zero parenting time multiplier.
  • Low-income obligors are safeguarded by the 75% poverty line Self-Support Reserve ($1,050/mo) and $40/child minimum order floor.
  • Out-of-pocket health insurance and childcare are apportioned strictly according to net income percentages.

Judicial Application & Controlling Case Law

Illinois judges apply the HFS schedule table without modification for non-shared physical care schedules.

Controlling Authority: 750 ILCS 5/505(a)(1); In re Marriage of Turk, 2014 IL 116730.

Practical Calculation Benchmark

Non-majority parent earning $5,000/mo net where majority parent earns $3,000/mo net (62.5% share) pays $1,303/month for 2 children ($2,085 schedule table).

Statutory Adjustment Guide

Allowable Income Deductions in Illinois

Under 750 ILCS 5/505, gross earnings are adjusted for mandatory expenses prior to applying the guideline schedule. The following statutory deductions reduce parental support obligations:

750 ILCS 5/505(a)(3)(C)

Federal and State Income Taxes

Standardized or individualized tax withholding, including Illinois state income tax (flat 4.95%).

750 ILCS 5/505(a)(3)(C)

FICA and Medicare Taxes

Mandatory Social Security and Medicare payroll tax deductions.

750 ILCS 5/505(a)(3)(C)

Mandatory Union Dues

Mandatory dues required as a condition of union employment.

750 ILCS 5/505(a)(3)(C)

Mandatory Retirement Contributions

Mandatory retirement or pension contributions required by law or contract.

750 ILCS 5/505(a)(3)(F)

Prior Court-Ordered Child Support Actually Paid

Court-ordered support payments for prior children from other relationships actually paid.

Judicial Discretion

Grounds for Departure from Illinois Guideline Math

Statutory child support formulas carry a rebuttable presumption of correctness. However, family court judges may depart from formula yields upon written findings of extraordinary circumstances:

⚖️ Shared Physical Care Multiplier (§ 505(a)(3.8))

Mandatory 1.5x gross-up calculation triggered when each parent exercises at least 146 overnights (40%).

⚖️ Extraordinary Healthcare Needs (§ 505(a)(2)(a))

Recurring medical or psychological expenses not covered by health insurance.

⚖️ Financial Resources of Child (§ 505(a)(2)(b))

Independent trust funds, settlement proceeds, or substantial minor earnings.

⚖️ Standard of Living During Marriage (§ 505(a)(2)(c))

Maintaining parity with the standard of living the child would have enjoyed had the marriage not dissolved.

⚖️ Physical and Emotional Condition (§ 505(a)(2)(d))

Specialized therapy, tutoring, or private educational accommodations.

Mathematical Case Study

Worked Case Example: Illinois Shared Physical Care 1.5x Multiplier (2 Children, 50/50 Custody)

Case Facts: Parent A earns $6,000/month net income. Parent B earns $4,000/month net income. The parents share 2 children with equal 50/50 time-sharing (183 overnights for Parent A, 182 overnights for Parent B).
Step 1: Determine Combined Net Income and SharesCombined Net = $6,000 + $4,000 = $10,000. Parent A = 60.0%, Parent B = 40.0%

Combine both parents’ net monthly incomes pursuant to 750 ILCS 5/505(a)(3).

Step 2: Extract Schedule Basic ObligationFrom HFS table: 2 children at $10,000 combined net = $2,460 / month

Reference the Illinois schedule of basic child support obligations.

Step 3: Apply 1.5x Shared Physical Care Multiplier$2,460 × 1.5 = $3,690.00 / month shared basic obligation

Under § 505(a)(3.8), because overnights exceed 146 (183 ≥ 146), base support is multiplied by 150%.

Step 4: Apportion Shared Obligation by Income SharesParent A Share = $3,690 × 60% = $2,214.00; Parent B Share = $3,690 × 40% = $1,476.00

Calculate each parent’s initial share of the shared care obligation.

Step 5: Multiply by Other Parent’s Time PercentageParent A to B = $2,214.00 × (182 / 365 = 49.86%) = $1,104.00; Parent B to A = $1,476.00 × (183 / 365 = 50.14%) = $739.99

Multiply each parent’s share by the time the child spends with the OTHER parent.

Step 6: Calculate Net Child Support OrderNet Payment = $1,104.00 - $739.99 = $364.01 / month (Parent A pays Parent B)

Parent A pays Parent B the net difference of $364/month.

💡 Calculated Judicial Order: Parent A pays $364/month to Parent B under Illinois’s statutory 1.5x Shared Physical Care formula.
State Legal Questions

Illinois Child Support Guidelines FAQ

How does Illinois calculate child support in 50/50 custody?

Under 750 ILCS 5/505(a)(3.8), when parents each have at least 146 overnights per year (40%), the court applies the Shared Physical Care formula. The basic support obligation is multiplied by 1.5 (150%) to account for duplicated household expenses. Each parent’s share is multiplied by the percentage of time the child spends with the OTHER parent, and the higher-obligation parent pays the net difference.

What is the 146 overnights rule in Illinois child support?

Under Illinois law (750 ILCS 5/505), 146 overnights represents 40% of the year. Reaching 146 overnights triggers the shared physical care formula, which substantially lowers child support obligations compared to the standard sole custody calculation.

How does Illinois handle high income over $30,000 per month?

For combined monthly net income exceeding $30,000 ($360,000 annually), Illinois courts apply the guideline support up to $30,000 plus statutory percentage additions or judicial discretion based on the child’s lifestyle and proven standard of living under § 505(a)(3.5).

How are health insurance and childcare costs credited in Illinois?

Under 750 ILCS 5/505(a)(3.6)-(3.7), child health insurance premiums and work-related childcare costs are added to the basic support obligation and divided between parents in proportion to their net incomes. The parent paying the provider receives a dollar-for-dollar credit.

Administrative & Interstate Framework

Illinois Title IV-D Agency & Interstate Support Framework

Official State Enforcement

Illinois Department of Healthcare and Family Services

Title IV-D child support services in Illinois are administered through the Illinois Department of Healthcare and Family Services. The agency manages automated income withholding, interstate order registration, federal parent locator queries (FPLS), and medical support enforcement under 750 ILCS 5/505.

Mandatory Court Worksheet: Shared Physical Care Child Support Worksheet (Form HFS 3989)
Interstate Moves & UIFSA

Continuing Exclusive Jurisdiction (CEJ)

If either parent or child relocates outside of Illinois, modification and collection proceedings are strictly governed by the Uniform Interstate Family Support Act (UIFSA, 42 U.S.C. § 666(f)) and the Full Faith and Credit for Child Support Orders Act (28 U.S.C. § 1738B).

Read Interstate Child Support & UIFSA Guide →