How Illinois Calculates Child Support for Two Children

Illinois does not set a fixed dollar amount for child support — the court calculates it based on both parents' income, custody time, and other factors specific to your case.

Illinois uses a income shares model, which means the court adds both parents' incomes together, finds what percentage of that combined income goes to child support, and then splits that obligation between parents based on how much each earns. For two children, the percentage of combined income that goes to support is typically between 20% and 25%, depending on whether there are other children in either household.

The actual dollar amount you or the other parent will pay depends entirely on what both of you earn. A parent earning $40,000 per year will pay a different amount than a parent earning $100,000 per year, even if both are supporting two children under the same custody arrangement.

Key Takeaways

• Illinois calculates child support as a percentage of combined parental income — typically 20% to 25% for two children — then divides that between parents based on their individual earnings.
• The amount changes if either parent's income changes significantly, if custody time shifts, or if a parent has other children from a different relationship.
• Child support continues until each child turns 18 or finishes high school, whichever is later, unless the child is still in high school after turning 18.
• The court can deviate from the standard percentage if factors like high income, low income, or substantial parenting time by the non-custodial parent explore.
• You can request a modification if circumstances change by more than 10% or if two years have passed since the last order.

How Illinois Calculates the Percentage

The Illinois Marriage and Dissolution of Marriage Act sets out a table of percentages. For two children, the standard is 20% of combined net income if the parents share custody roughly equally, or if one parent has primary custody. If the non-custodial parent has the children more than 40% of the time, the percentage may shift slightly.

Here is how it works in practice: if Parent A earns $50,000 per year and Parent B earns $30,000 per year, the combined income is $80,000. Twenty percent of $80,000 is $16,000 per year, or about $1,333 per month. Parent A, who earns 62.5% of the combined income, would pay roughly $1,000 per month. Parent B, who earns 37.5%, would pay roughly $333 per month — but only if Parent B has custody less than 40% of the time.

The court starts with net income, not gross income. Net income means gross income minus taxes, union dues, health insurance premiums, and certain other deductions. Self-employed parents must subtract business expenses. The exact calculation depends on what documents you bring to court.

When Custody Time Changes the Amount

If both parents share custody roughly equally — meaning each parent has the children at least 40% of the time — the calculation shifts. Instead of one parent paying the other, both parents' support obligations are calculated, and the parent with the higher obligation pays the difference to the other parent.

For example, if Parent A earns $60,000 and Parent B earns $40,000, and they split custody 50-50, the court calculates what each parent owes based on 20% of combined income. Parent A's obligation is higher because Parent A earns more, so Parent A pays the difference to Parent B. The parent with less custody time does not automatically pay more — the higher earner pays more.

If one parent has the children significantly more than 40% of the time — say, 70% — that parent's support obligation is reduced or eliminated, because they are already spending money directly on the children's food, housing, and activities during their parenting time.

Income Limits and High-Income Adjustments

Illinois sets a cap on the income used in the standard calculation. As of 2024, that cap is $240,000 in combined net income. If both parents together earn more than $240,000, the court can still order support above the standard percentage, but it has discretion to do so and must consider factors like the children's standard of living, the parents' ability to pay, and other support obligations.

For parents with very high income, the court often orders support that exceeds the standard percentage to maintain the children's accustomed standard of living. For parents with very low income, the court may order less than the standard percentage or may find that one parent cannot pay at all.

If one parent is unemployed or underemployed, the court may impute income — meaning it assumes the parent could earn more and calculates support based on that assumed income. The court looks at the parent's education, work history, and job market to decide what income to impute. A parent cannot straightforward quit a job to avoid child support.

Other Children and Support Obligations

If either parent has other children from a different relationship and is already paying or receiving child support for those children, the court may adjust the calculation. A parent who is already paying support for three children from a previous relationship may have a lower obligation for the two children in your case.

The court uses the same income shares model for all children but calculates the percentage based on how many children are in the household. The percentage increases as the number of children increases: 17% for one child, 20% for two children, 22% for three children, 25% for four children, and 28% for five or more children.

When Support Ends

Child support in Illinois continues until each child turns 18, unless the child is still enrolled in high school. If a child is still in high school after turning 18, support continues until the child graduates or turns 19, whichever comes first.

Support also ends if the child becomes emancipated — meaning the child marries, joins the military, or is declared independent by the court. Support does not automatically end if the child moves out or stops living with the custodial parent; the parent receiving support must request a modification.

Modifying the Amount

Either parent can request a modification if circumstances change. Illinois law allows modification if there has been a substantial and continuing change in circumstances — typically defined as a change in either parent's income of at least 10%, or a significant change in custody time.

You do not have to wait for a specific event to request modification. If two years have passed since the last support order, either parent can request a review and potential adjustment based on current income. If one parent's income has dropped by 15% due to job loss, or increased by 20% due to a promotion, that is grounds for modification.

To request modification, you file a petition with the court that issued the original order. You will need to provide recent pay stubs, tax returns, and documentation of the change in circumstances. The other parent has the right to respond and present their own financial information.

Frequently Asked Questions

What if one parent makes significantly more than the other?

The higher earner pays a larger share of the support obligation because the calculation is based on each parent's percentage of combined income. If one parent earns $80,000 and the other earns $20,000, the higher earner pays 80% of the total support obligation. The court does not equalize income; it divides the obligation proportionally.

Does child support change automatically when a child turns 18?

No. Support continues if the child is still in high school. Once the child graduates or turns 19, whichever comes first, the obligation ends for that child. The parent receiving support does not need to notify the court; the obligation straightforward stops. However, if the other child is still a minor, support continues for that child.

Can the court order more than the standard percentage for two children?

Yes. The court can deviate from the 20% standard if factors like high income, low income, substantial parenting time by the non-custodial parent, or other children's support obligations explore. The court must state its reasons in writing if it orders an amount different from the standard calculation.

What counts as income for child support purposes?

Income includes wages, salary, bonuses, commissions, self-employment income, rental income, investment income, and certain benefits. It does not include means-tested benefits like SNAP or TANF, or child support received from another relationship. The court looks at tax returns and recent pay stubs to verify income.

What happens if the paying parent loses their job?

The paying parent can request a modification, but must do so promptly and provide documentation of the job loss. The court will not automatically reduce support; the parent must file a petition. If the parent straightforward stops paying without requesting modification, the other parent can pursue enforcement, including wage garnishment and contempt charges.