Support in Illinois (2026)

The Illinois Statutory Maintenance Formula

One of the most distinctive features of Illinois family law is its detailed statutory formula for spousal maintenance, codified in 750 ILCS 5/504. Unlike many states where judges have broad discretion over the amount and duration of alimony, Illinois provides a specific mathematical framework that applies in most cases.

The formula works as follows: the maintenance amount equals 33.33% of the payor’s net income minus 25% of the payee’s net income. However, this amount is subject to a critical cap — when combined with the payee’s net income, the maintenance payment cannot exceed 40% of the parties’ combined net income. This cap ensures that the recipient does not end up with a higher standard of living post-divorce than during the marriage.

The formula applies when the combined gross income of both spouses is $500,000 or less. For higher-income cases, the court has discretion to set maintenance based on the statutory factors listed in Section 504(a) without being bound by the formula.

Equally important is the duration component. Illinois ties the length of maintenance to the length of the marriage using statutory multipliers:

• Marriage under 5 years: Duration = 20% of the marriage length
• 5-6 years: 40%
• 6-7 years: 44%
• 7-8 years: 48%
• 8-9 years: 52%
• 9-10 years: 56%
• 10-11 years: 60%
• 11-12 years: 64%
• 12-13 years: 68%
• 13-14 years: 72%
• 14-15 years: 76%
• 15-16 years: 80%
• 16-17 years: 84%
• 17-18 years: 88%
• 18-19 years: 92%
• 19-20 years: 96%
• 20 or more years: The court may order maintenance for a period equal to the marriage length or for an indefinite term

This formula-based approach gives both parties a clearer picture of potential outcomes early in the process, which can facilitate settlement negotiations. Courts retain discretion to deviate from the formula when circumstances make the result unjust, but in practice, the formula anchors most maintenance outcomes in Illinois.

How Illinois Calculates Child Support

Since a major reform in 2017, Illinois has used an income shares model for child support. This replaced the older percentage-of-income method and brought Illinois in line with the majority of states. The current framework is codified in 750 ILCS 5/505.

Under the income shares model, the court determines each parent’s net income, combines them, and then consults a guideline table that specifies the basic support obligation based on the combined net income and the number of children. Each parent’s share of the total obligation is proportional to their share of combined net income.

Net income is calculated by subtracting standardized taxes (federal, state, FICA, and Medicare) from gross income, along with certain other deductions. Illinois uses a standardized tax approach rather than actual tax withholdings to ensure consistency across cases.

For a broader overview of how income shares models work in different states, see our guide on how child support is calculated.

Key Components of the Calculation

The Illinois child support guidelines consider several factors beyond base income:

• Both parents’ gross income. This includes wages, salary, commissions, bonuses, severance pay, pensions, annuities, Social Security benefits, disability benefits, trust income, interest, dividends, rental income, business income, and any other source of recurring income.
• Imputed income. If a parent is voluntarily unemployed or underemployed, the court may impute income based on that parent’s employment potential, recent work history, and earning capacity.
• Child care expenses. Costs for child care necessary for either parent to work or attend school are added to the base support obligation and divided proportionally.
• Health insurance premiums. The cost of maintaining health insurance coverage for the child is added to the basic obligation.
• Extraordinary expenses. These may include special educational needs, extracurricular activities agreed upon by both parents, or recurring medical expenses not covered by insurance.

Shared Parenting Adjustment

Illinois provides a specific adjustment for shared parenting situations. When each parent exercises 146 or more overnights per year (40% or more of the time), the shared parenting formula applies. Under this formula, each parent’s child support obligation is calculated individually based on their income and the number of overnights, and the obligations are then offset against each other. The parent with the higher obligation pays the difference to the other parent.

This adjustment recognizes that parents who share significant time with their children incur substantial direct costs during their parenting time, and it prevents the duplication of expenses.

You can estimate your potential obligation using our child support calculator.

Modifying Child Support in Illinois

A parent may petition for modification of child support by demonstrating a substantial change in circumstances. Illinois also allows modification if the existing order was entered at least three years ago and applying the current guidelines to the parties’ present incomes would result in a change of at least 10% (either up or down) from the current order.

Modifications take effect only from the date the petition is filed — arrears that accrued before the petition date cannot be reduced retroactively.

Child support in Illinois ordinarily continues until the child turns 18, or until age 19 if the child is still attending high school. The court may also order support for a non-minor child attending college or trade school, covering a reasonable portion of tuition, room and board, and other educational expenses. This is a notable feature of Illinois law that does not exist in many other states.

Enforcement of Child Support Orders

Illinois enforces child support orders through the Division of Child Support Services, which has access to multiple enforcement tools:

• Income withholding notices (mandatory in most cases)
• Interception of federal and state tax refunds
• Liens on real property, vehicles, and financial accounts
• Suspension of driver’s licenses, professional licenses, and recreational licenses
• Reporting to credit bureaus
• Contempt of court, which can lead to fines or incarceration
• Passport denial for arrears exceeding $2,500

Illinois imposes 9% annual interest on unpaid child support, providing a strong incentive for timely payment.

Factors Influencing Maintenance

Beyond the formula, the court considers factors listed in 750 ILCS 5/504, including:

• Each party’s income and property
• The needs of each party
• The present and future earning capacity of each party
• Any impairment of earning capacity due to devoting time to domestic duties or forgoing education or career opportunities for the benefit of the other spouse
• The time necessary for the payee to acquire education, training, or employment
• The standard of living established during the marriage
• The duration of the marriage
• The age and health of both parties
• Tax consequences of the property division
• Contributions and services by the payee to the payor’s education, training, career, or license
• Any valid prenuptial or postnuptial agreement

Types of Maintenance in Illinois

Illinois recognizes several categories of maintenance under 750 ILCS 5/504:

• Temporary maintenance — awarded during the divorce proceedings to maintain the status quo
• Fixed-term (reviewable) maintenance — awarded for a specific period, subject to review at the end of the term
• Indefinite maintenance — typically reserved for marriages of 20 years or longer, or when circumstances make a termination date inappropriate
• Permanent maintenance — ordered when the court determines that the payee will never achieve financial independence due to age, disability, or other factors

The distinction between these types matters for modification purposes. Fixed-term maintenance is subject to review at the end of its term, while indefinite or permanent maintenance continues until death, remarriage of the payee, or cohabitation on a continuing conjugal basis.

When to Seek Legal Guidance

Illinois family law provides relatively clear formulas for both child support and maintenance, but the interplay between the two — particularly in shared parenting arrangements or cases involving high income, self-employment, or business ownership — can create complexity. If you are facing a support dispute or seeking to understand your potential obligations, consider scheduling a free consultation to discuss your situation with a family law professional.

Statutes referenced: 750 ILCS 5/505 (child support), 750 ILCS 5/504 (maintenance).

Frequently Asked Questions

How is child support calculated in Illinois?

Illinois uses the income shares model under 750 ILCS 5/505, adopted in 2017. Each parent’s net income (gross income minus standardized taxes) is combined and applied to a guideline table based on combined income and number of children. Each parent’s share is proportional to their percentage of combined net income. Childcare costs, health insurance premiums, and extraordinary expenses are added and divided proportionally.

How long does child support last in Illinois?

Child support continues until the child turns 18, or until age 19 if the child is still attending high school. Illinois courts may also order support for a non-minor child attending college or trade school, covering tuition, room and board, and educational expenses — a notable feature not available in many states. Unpaid support accrues 9% annual interest.

How does shared parenting affect child support in Illinois?

When each parent has 146 or more overnights per year (40% or more), the shared parenting formula applies. Each parent’s support obligation is calculated individually based on income and overnights, then offset so the parent with the higher obligation pays the difference. This prevents duplication of expenses across households.

What is the Illinois maintenance formula?

The formula is 33.33% of the payor’s net income minus 25% of the payee’s net income, capped so the payee’s total income does not exceed 40% of the parties’ combined net income. Duration is tied to marriage length by statutory multiplier (e.g., 20% for marriages under 5 years, up to indefinite for 20+ years). The formula applies when combined gross income is under $500,000.

Can Illinois courts order a parent to pay for college?

Yes. Under 750 ILCS 5/513, Illinois is one of a limited number of states where courts can order a parent to contribute to a non-minor child’s college or vocational education expenses. The court considers factors including the financial resources of both parents, the child’s academic performance, and the standard of living the child would have enjoyed had the marriage not been dissolved. This authority is notable because most states end parental support obligations at age 18 or high school graduation.

What happens to maintenance if I start living with a new partner?

Under 750 ILCS 5/510(c), maintenance terminates upon the recipient’s remarriage or if the recipient cohabits with another person on a “resident, continuing conjugal basis.” The payor must petition the court and demonstrate the cohabitation. Courts look at factors such as shared living expenses, the duration of the relationship, and whether the arrangement is essentially equivalent to marriage. A casual dating relationship would typically not qualify.

How This Guide Was Researched

This guide was compiled through a detailed review of the Illinois child support and maintenance statutes within the Illinois Marriage and Dissolution of Marriage Act (750 ILCS 5/). The income shares model provisions were verified against 750 ILCS 5/505 and the standardized guideline tables published by the Illinois Department of Healthcare and Family Services. The maintenance formula, including the amount calculation, the 40% cap, and the duration multipliers, was confirmed against 750 ILCS 5/504(b-1). Enforcement mechanisms were cross-referenced with information from the Illinois Division of Child Support Services and the Illinois Courts self-help portal.

Sources and Legal References

This guide draws on the following Illinois statutes and official resources:

• 750 ILCS 5/504 — Maintenance; statutory formula for amount and duration, the 40% income cap, and the duration multipliers tied to marriage length
• 750 ILCS 5/504(b-1) — Duration of maintenance based on statutory multipliers
• 750 ILCS 5/505 — Child support; income shares model, guideline tables, and standardized net income calculations
• 750 ILCS 5/510 — Modification and termination of maintenance and support; substantial change in circumstances standard
• 750 ILCS 5/513 — Support for non-minor children; college and vocational education expenses

Official Illinois Resources

• Illinois Courts — Self-Help
• Illinois Divorce, Child Support & Maintenance Forms

For more about how we research our guides, see our editorial policy and sources methodology.

Related Guides

Illinois Support Guides

• Illinois Maintenance Calculation
• Imputing Income for Child Support in Illinois

Other Illinois Family Law Guides

• Divorce in Illinois
• Child Custody in Illinois

National Guides

• How Child Support Is Calculated
• How Alimony Works
• How Alimony Is Calculated
• Property Division in Divorce