Illinois calculates child support using the income shares model under 750 ILCS 5/505, which combines both parents' net incomes, references the Schedule of Basic Child Support Obligations, and divides the obligation proportionally based on each parent's share of combined income. For two parents earning a combined $10,000 per month with two children, the basic support obligation is approximately $2,068 per month, split according to each parent's percentage of that combined income. The Illinois Department of Healthcare and Family Services (HFS) updates the obligation schedule annually, with the most recent update effective March 5, 2025.
Key Facts: Illinois Child Support
| Factor | Details |
|---|---|
| Governing Statute | 750 ILCS 5/505 |
| Calculation Model | Income Shares (effective July 1, 2017) |
| Filing Fee | $210 to $388, depending on county |
| Residency Requirement | 90 days for at least one spouse |
| Waiting Period | None (eliminated in 2016) |
| Grounds for Divorce | No-fault only (irreconcilable differences) |
| Property Division | Equitable distribution |
| Child Support Duration | Until age 18 (or 19 if still in high school) |
| Shared Parenting Threshold | 146 overnights per year |
| Schedule Updates | Annual (most recent: March 5, 2025) |
How Does the Illinois Child Support Calculator Work?
The Illinois child support calculator uses the income shares model to estimate each parent's financial obligation based on combined net income, number of children, and parenting time allocation. Under 750 ILCS 5/505(a)(1), the court determines support by computing both parents' monthly net incomes, combining them, referencing the Schedule of Basic Child Support Obligations published by the Illinois Department of Healthcare and Family Services, and allocating the obligation proportionally. This method replaced the older percentage-of-obligor-income model on July 1, 2017.
The calculation follows a four-step statutory formula:
- Determine each parent's monthly net income by subtracting federal and state income taxes, FICA, mandatory retirement contributions, union dues, and existing support obligations for other children from gross income
- Add both parents' monthly net incomes together to reach the combined monthly net income
- Locate the basic child support obligation on the HFS Schedule of Basic Child Support Obligations using the combined monthly net income and number of children
- Calculate each parent's percentage share of the combined net income, then multiply that percentage by the basic support obligation to determine each parent's share
The parent with fewer overnights typically pays their share to the custodial parent. Illinois courts retain discretion to deviate from the guidelines under 750 ILCS 5/505(a)(2) when application would be inequitable, unjust, or inappropriate.
What Income Counts for Illinois Child Support Calculations?
Illinois child support calculations include all income from all sources under 750 ILCS 5/505(a)(3), encompassing wages, salaries, commissions, bonuses, self-employment earnings, pensions, Social Security benefits, unemployment compensation, disability payments, rental income, and investment returns. The statute defines gross income broadly to capture the full financial picture of each parent's earning capacity.
Income sources included in the child support worksheet:
- Salary, wages, tips, and overtime pay
- Commissions, bonuses, and profit-sharing distributions
- Self-employment income (net of legitimate business expenses)
- Severance pay and back pay awards
- Social Security benefits and disability payments
- Pension and retirement fund distributions
- Unemployment and workers' compensation benefits
- Annuity and trust income
- Capital gains and dividends
- Rental income from real or personal property
- Spousal maintenance received from a prior marriage
The court may also impute income to a parent who is voluntarily unemployed or underemployed. Under 750 ILCS 5/505(a)(3.3), if a parent is found to be voluntarily unemployed, the court calculates child support based on that parent's potential income, considering prior employment history, education, and available job opportunities in the local economy.
How Does Parenting Time Affect Child Support in Illinois?
Illinois adjusts child support calculations when both parents exercise at least 146 overnights per year (40% of the time), triggering the shared parenting formula under 750 ILCS 5/505(a)(1.5). Under this formula, the basic child support obligation is multiplied by 1.5 to account for duplicated household expenses, and each parent's proportional share is offset based on the percentage of time each parent spends with the child.
The shared parenting calculation works as follows:
- Calculate the basic child support obligation using the standard income shares method
- Multiply that obligation by 1.5 to reach the shared care support obligation
- Multiply each parent's proportional share by the percentage of time the child spends with the other parent
- Offset the two amounts, with the parent owing more paying the difference
For example, if the basic obligation is $1,800 per month for two children, the shared care obligation becomes $2,700 ($1,800 multiplied by 1.5). If Parent A earns 60% of the combined income and has 55% of overnights, while Parent B earns 40% and has 45% of overnights, the offset calculation produces a substantially lower payment than the standard formula. Parents with fewer than 146 overnights per year use the standard calculation without the 1.5 multiplier or offset.
What Additional Expenses Are Added to Child Support?
Illinois courts add healthcare premiums, unreimbursed medical expenses, and work-related childcare costs to the basic child support obligation under 750 ILCS 5/505(a)(4). These additional expenses are divided between parents in proportion to their respective shares of combined net income, and they are added on top of the basic support obligation from the Schedule of Basic Child Support Obligations.
Additional expenses typically ordered by Illinois courts:
| Expense Category | How Divided | Statutory Basis |
|---|---|---|
| Health insurance premiums for the child | Proportional to income | 750 ILCS 5/505(a)(4) |
| Unreimbursed medical, dental, and vision costs | Proportional to income | 750 ILCS 5/505(a)(4) |
| Work-related childcare (daycare, after-school care) | Proportional to income | 750 ILCS 5/505(a)(4) |
| Education-related childcare (while parent attends school) | Proportional to income | 750 ILCS 5/505(a)(4) |
| Extracurricular activity expenses | Court discretion | 750 ILCS 5/505(a)(2) |
| Private school tuition | Court discretion, if in child's best interest | 750 ILCS 5/505(a)(2) |
For healthcare costs, the basic child support obligation already includes an allowance for ordinary out-of-pocket medical expenses of $250 per child per year. Unreimbursed medical costs exceeding that threshold are divided proportionally between both parents. Childcare expenses must be reasonable and necessary to enable a parent to maintain employment or pursue education that improves employment opportunities.
How to Use the Official Illinois Child Support Estimator
The Illinois Department of Healthcare and Family Services provides a free online child support estimator at hfs.illinois.gov that generates estimates based on the current Schedule of Basic Child Support Obligations and the Gross to Net Income Conversion Table. The HFS estimator offers two versions: a guided question-and-answer format for parents and a direct-entry format for legal professionals. Both versions apply the same statutory formula under 750 ILCS 5/505.
To calculate child support using the HFS estimator, gather the following information before starting:
- Both parents' gross monthly income from all sources (pay stubs, tax returns, Social Security statements)
- Federal and state tax filing status for each parent
- Number of children from this relationship requiring support
- Number of other children each parent is legally obligated to support
- Monthly health insurance premium cost for the children
- Monthly work-related childcare costs
- Number of overnights per year each parent exercises (or will exercise under the parenting plan)
The estimator will convert gross income to net income using the standardized conversion table, look up the basic obligation on the schedule, allocate shares based on each parent's percentage of combined income, and apply the shared parenting adjustment if applicable. The result is an estimate only; the court retains authority to deviate from the guidelines based on factors listed in 750 ILCS 5/505(a)(2).
When Can Illinois Courts Deviate from Child Support Guidelines?
Illinois courts may deviate from the child support guidelines when strict application would be inequitable, unjust, or inappropriate, but the court must issue written findings explaining the deviation and stating what the guideline amount would have been under 750 ILCS 5/505(a)(2). Deviations are not automatic; the parent requesting the deviation bears the burden of demonstrating that specific circumstances justify a departure from the calculated amount.
Statutory factors that may justify deviation from the child support worksheet:
- Extraordinary medical expenses necessary to preserve the life or health of a parent or child
- Additional expenses for a child with special medical, physical, or developmental needs
- The financial resources and needs of the child beyond the basic obligation
- The financial resources and needs of each parent
- The standard of living the child would have enjoyed had the marriage not been dissolved
- The physical and emotional condition of the child
- The educational needs of either parent that would increase future earning capacity
- Tax consequences of the support allocation to each parent
- Pre-existing support obligations for other children or former spouses
- Expenses related to the child's education, including private school or tutoring if previously agreed upon by the parents
The court must document the specific reasons for any deviation and calculate the presumptive guideline amount for the record. Either parent may seek modification of a deviated order if circumstances change substantially.
How to Modify an Existing Illinois Child Support Order
Illinois allows modification of child support orders when a substantial change in circumstances has occurred since the original order, or when the existing order has been in effect for at least 3 years and the current guidelines would result in a change of at least 20% under 750 ILCS 5/510. Filing a motion to modify child support in Illinois requires paying a motion fee of approximately $60 to $80, depending on the county.
Common grounds for child support modification in Illinois:
- A significant increase or decrease in either parent's income (job loss, promotion, disability)
- A change in the number of overnights exercised by either parent
- A change in the child's healthcare needs or educational expenses
- Emancipation of one child when multiple children are covered by the order
- A change in either parent's support obligations for other children
- The 3-year/20% automatic review threshold under 750 ILCS 5/510(a)(1)
The modification process typically takes 2 to 4 months if both parents agree and 4 to 8 months if contested. Either parent can file a petition for modification with the circuit court in the county where the original order was entered. The Illinois Department of Healthcare and Family Services can also initiate a review of child support orders every 3 years upon request by either parent.
What Happens When Combined Income Exceeds the Illinois Guidelines Table?
Illinois courts exercise discretion when combined adjusted net income exceeds the highest level on the Schedule of Basic Child Support Obligations, which currently tops out at $30,000 per month in combined net income under 750 ILCS 5/505(a)(1)(B). For high-income families earning above this threshold, the court is not required to follow the schedule and instead considers the child's needs and the parents' ability to pay.
For families with combined monthly net income above $30,000, Illinois courts typically:
- Apply the guidelines amount for the portion of income up to $30,000
- Use judicial discretion for income above $30,000, considering the child's actual needs and accustomed standard of living
- Review evidence of the child's actual expenses, including housing, education, extracurricular activities, travel, and healthcare
- Consider the lifestyle the child would have experienced in an intact household
The court will not simply extrapolate the guidelines table upward. Instead, the requesting parent must present evidence of the child's reasonable needs, and the court balances those needs against both parents' financial resources. High-income child support disputes frequently require forensic accountants and detailed expense documentation.
How Does Illinois Handle Child Support for Self-Employed Parents?
Illinois calculates child support for self-employed parents by using net self-employment income after deducting legitimate and necessary business expenses, but courts scrutinize deductions for personal expenses disguised as business costs under 750 ILCS 5/505(a)(3). Self-employed parents must provide complete tax returns, profit-and-loss statements, and business bank records for at least the previous 2 to 3 years.
Key considerations for self-employed parent child support calculations:
- Courts examine tax returns (Schedule C, K-1, or corporate returns) for the most recent 2 to 3 years to establish average income
- Depreciation and other non-cash deductions may be added back to income because they reduce tax liability without reducing actual cash available
- Personal expenses run through a business (vehicle payments, meals, travel, home office deductions) may be added back to income
- Courts may impute income based on earning capacity if a self-employed parent appears to be suppressing income through the business
- The court may average income over multiple years to account for annual fluctuations in self-employment earnings
- Business valuation experts or forensic accountants may be appointed when income is difficult to determine
The Illinois child support calculator requires accurate net income inputs to produce reliable estimates. Self-employed parents should work with a family law attorney to prepare a child support worksheet that accurately reflects their income after legitimate business deductions but before discretionary personal expenses.
Filing for Child Support in Illinois: Costs and Process
Filing a petition for child support in Illinois costs between $210 and $388 depending on the county, with Cook County charging $388 and DuPage County charging $348 as of early 2026. An appearance or response fee adds approximately $251 in Cook County. Parents who cannot afford filing fees may request a fee waiver if household income falls at or below 125% of the federal poverty guidelines.
The child support filing process in Illinois follows these steps:
- File a Petition for Dissolution of Marriage or a standalone Petition for Child Support with the circuit court in the county where either parent resides
- Pay the filing fee ($210 to $388 depending on county)
- Serve the other parent with the petition and summons through the county sheriff or a private process server
- Both parents complete and exchange Financial Affidavits disclosing all income, assets, and debts
- Both parents complete the Illinois Child Support Worksheet using the income shares model
- Attend a case management conference or hearing where the court reviews the child support calculation
- The court enters a child support order based on the guidelines or approved agreement
Illinois requires at least one spouse to have been a resident of the state for 90 consecutive days before a divorce can be finalized. Child support orders are enforceable through wage garnishment, tax refund intercept, license suspension, and contempt of court proceedings.
Frequently Asked Questions About the Illinois Child Support Calculator
How is child support calculated in Illinois in 2026?
Illinois uses the income shares model under 750 ILCS 5/505 to calculate child support. Both parents' net incomes are combined, the basic obligation is found on the HFS Schedule of Basic Child Support Obligations (updated March 5, 2025), and each parent pays their proportional share. Additional costs for healthcare and childcare are divided on top of the basic obligation.
What is the minimum child support payment in Illinois?
Illinois does not set a fixed minimum child support amount by statute. The income shares model under 750 ILCS 5/505 produces a calculated amount based on both parents' incomes and the number of children. For very low combined incomes (under $1,200 per month), the Schedule of Basic Obligations provides reduced amounts, and courts may set nominal support as low as $10 to $50 per month.
Does 50/50 custody eliminate child support in Illinois?
Equal parenting time does not automatically eliminate child support in Illinois. When both parents have at least 146 overnights per year, the shared parenting formula under 750 ILCS 5/505(a)(1.5) applies, multiplying the basic obligation by 1.5 and offsetting each parent's share. If one parent earns significantly more, they will still owe child support even with a 50/50 parenting schedule.
How long does child support last in Illinois?
Illinois child support continues until the child turns 18 years old, or until age 19 if the child is still attending high school, whichever comes first. Under 750 ILCS 5/505(g), the court may also order support for a non-minor disabled child who is unable to support themselves. College education expenses may be ordered separately under 750 ILCS 5/513.
Can Illinois child support be modified after the order is entered?
Yes. Illinois allows child support modifications when a substantial change in circumstances occurs, or after 3 years if the current guidelines produce an amount at least 20% different from the existing order under 750 ILCS 5/510. Common triggers include job loss, significant income change, change in parenting time, or a child's changed needs. The modification filing fee is approximately $60 to $80.
Does overtime count as income for Illinois child support?
Overtime pay is included as income for Illinois child support calculations under 750 ILCS 5/505(a)(3). Courts typically average overtime earnings over the most recent 2 to 3 years rather than using a single pay period. If overtime is sporadic or seasonal, the court may use a longer averaging period to establish a reliable income figure.
What happens if a parent does not pay child support in Illinois?
Illinois enforces child support orders through multiple mechanisms under 750 ILCS 5/505(d): income withholding (wage garnishment), tax refund intercept, suspension of driver's license, suspension of professional licenses, passport denial for arrearages exceeding $2,500, bank account liens, and contempt of court proceedings that can result in fines or incarceration for willful non-payment.
How does remarriage affect child support in Illinois?
Remarriage alone does not change a child support obligation in Illinois. Under 750 ILCS 5/505, only the biological or adoptive parents' incomes are used in the child support calculation. A new spouse's income is not included in the child support worksheet. However, if remarriage significantly changes a parent's financial circumstances (such as reduced living expenses), the court could consider that factor when evaluating a modification request.
Can parents agree to a different child support amount in Illinois?
Parents may agree to a child support amount different from the guidelines, but the court must approve the agreement under 750 ILCS 5/502(a). The court will review whether the agreed amount adequately provides for the child's needs. If the agreed amount is significantly below the guidelines, the court may reject the agreement and order the guideline amount instead. Parents cannot waive child support entirely, as the right to support belongs to the child.
Where can I find the official Illinois child support estimator?
The Illinois Department of Healthcare and Family Services provides a free online child support estimator at hfs.illinois.gov. The estimator uses the current Schedule of Basic Child Support Obligations and the Gross to Net Income Conversion Table (both updated annually, most recently March 5, 2025). HFS offers two versions: a question-and-answer format for parents and a direct-entry format for legal professionals.
Note: Filing fees cited are as of early 2026. Verify current amounts with your local circuit clerk's office before filing.