When couples separate or divorce, two of the most important financial issues they face are determining child support and spousal maintenance (sometimes referred to as alimony).
Illinois sets clear statutory guidelines to ensure fairness and consistency in family law cases. These guidelines, codified in the Illinois Marriage and Dissolution of Marriage Act, provide formulas that courts use to calculate support obligations. However, judges retain some flexibility to deviate when circumstances warrant.
If you are considering divorce, separation, or a support modification in the Prairie State, understanding these rules is the first step toward clarity during a difficult time.
Illinois’s Income Shares Model for Child Support
Since July 1, 2017, Illinois has used the “income shares model” for calculating child support, which is based on the principle that children should receive the same proportion of parental income they would have received if the family remained intact.
This model considers both parents’ combined net income rather than focusing solely on the non-custodial parent’s earnings.
The income shares approach represents a significant philosophical shift. Rather than treating child support as a one-way payment, it recognizes that both parents contribute financially to their children’s well-being: one through direct payments and the other through day-to-day expenses.
How the Calculation Works
The calculation process begins by determining each parent’s monthly net income, then combining these amounts to establish a total from which the support obligation is proportionally divided according to a predetermined schedule outlined in 750 ILCS 5/505(a)(1.5).
Each parent’s share of the support obligation corresponds to their percentage of the combined net income. The parent with less parenting time typically pays their calculated share to the parent with more parenting time.
Defining Income for Child Support Purposes
Under Illinois law, “gross income” means the total of all income from all sources, with specific exceptions for public assistance benefits like Temporary Assistance for Needy Families and Supplemental Security Income.
The law allows deductions for federal and state income taxes, Social Security contributions, mandatory retirement contributions, prior child support or maintenance obligations actually paid, and certain other expenses directly related to producing income or maintaining health.
For very low-income parents whose actual or potential income is no more than 75% of the federal poverty guidelines for a single-person household, Illinois law presumes a minimum support obligation of at least $40 per month per child, up to a maximum of $120 monthly for all children, though exceptions apply for incarcerated parents and those unable to work due to disability.
When Courts Deviate from Guidelines
While the statutory guidelines provide the starting point, courts may deviate after considering factors including the financial resources and needs of both the child and parents, the standard of living the child would have enjoyed had the marriage not dissolved, and the child’s physical, emotional, and educational needs, as outlined in 750 ILCS 5/505(a)(2).
Judges must explain in writing why they’re departing from the guideline amount, ensuring accountability and providing a clear record for any potential appeals.
Illinois Spousal Maintenance (Alimony) Guidelines
Spousal maintenance, formerly called alimony, is governed by statute 750 ILCS 5/504. The purpose is to ensure that a lower-earning spouse can maintain financial stability post-divorce. In most cases, maintenance is not automatic; courts evaluate many statutory factors to determine if it is appropriate.
The statutory factors for determining spousal maintenance (alimony) in Illinois include:
- Length of marriage
- Each party’s income and future earning capacity
- Age and health of both parties
- Standard of living established during the marriage
- Contributions as a homemaker or to the other spouse’s career or education
- Impairment of earning capacity
- Any prior agreement (e.g., prenups or postnups)
How Maintenance is Calculated
If maintenance is deemed appropriate, Illinois uses a formula:
- Amount: 33⅓% of the payor’s net annual income minus 25% of the recipient’s net annual income. The maintenance amount, when added to the recipient’s income, cannot exceed 40% of the combined net incomes.
- Duration: Determined by multiplying the length of the marriage by increasingly larger percentages (for example, 20% for marriages less than 5 years, up to 80% for marriages of 20 years or more, which may be permanent or indefinite).
This formula recognizes that both spouses contributed to the marital standard of living and aims to allow both parties to maintain a reasonable lifestyle post-divorce, while preventing windfall payments that would give the recipient a disproportionate share of the combined income.
Recent Maintenance Law Changes
As of January 2025, Illinois no longer allows maintenance obligations to be automatically paused if the payor is incarcerated. A judge must find a compelling reason to pause or modify payments.
Maintenance is always based on the net, not gross, income, for greater fairness. Courts must specifically state when they deviate from guidelines and explain their reasoning in writing.
Illinois law recognizes several types of maintenance designations. Fixed-term maintenance establishes a specific end date, after which maintenance is barred. Indefinite maintenance has no predetermined termination date. Reviewable maintenance allows the court to reassess the appropriateness of maintenance at a specified future date.
Why Legal Guidance Matters
Understanding the statutory formulas is valuable, but applying them correctly requires careful attention to how income is defined and calculated, which deductions are permissible, how assets factor into the analysis, and when circumstances justify deviating from guidelines.
Small differences in how income is characterized or which deductions are claimed can significantly impact support obligations.
An experienced and compassionate family law advocate can help ensure that income is properly calculated, all relevant factors are presented to the court, any grounds for deviation from guidelines are identified and argued effectively, and support orders are drafted clearly to prevent future disputes.
If you’re facing a support or maintenance issue in Illinois, you don’t have to navigate it alone. The right legal, financial, and strategic guidance can make all the difference. We’re here to help — schedule a confidential consultation today!
