Illinois uses a formula based on both parents' income

Illinois child support is not a fixed dollar amount — it depends on how much each parent earns, how many children need support, and how much time each parent spends with the children. The state uses what's called the Income Shares Model, which means the court calculates what percentage of combined parental income should go toward child support, then divides that amount between the parents based on their individual earnings.

The starting point is always the parents' gross monthly income. "Gross" means before taxes and deductions. The court adds both parents' incomes together, then looks up that combined total on the state's child support guidelines table to find the base support amount. From there, the calculation adjusts based on each parent's share of the total income and custody arrangement.

No two cases produce the same number because no two families have identical incomes or parenting schedules. A parent earning $3,000 per month with one child will owe a different amount than a parent earning $5,000 per month with two children.

Key Takeaways

  • Illinois calculates child support by combining both parents' gross monthly income, looking up the total on the state guidelines table, then dividing the obligation based on each parent's percentage of that combined income.
  • The guidelines table sets a base amount for different income levels and numbers of children, ranging from roughly $500 to $2,000+ per month depending on combined income and child count.
  • The parent with primary custody usually receives support; the parent with less time pays; if custody is split roughly equally, the higher earner typically pays the difference.
  • The court can adjust the guideline amount up or down if either parent earns over $240,000 annually, has significant assets, or if there are other children from different relationships.
  • Child support continues until the child turns 18, or 19 if still in high school, unless the child is emancipated or adopted by someone else.

What the Illinois guidelines table shows

The state publishes a table that lists base child support amounts for different combined income levels and different numbers of children. The table starts at combined incomes around $1,000 per month and goes up to $240,000 per month. For example, if two parents together earn $4,000 per month and have one child, the table might show a base obligation of around $800 to $900 per month (exact figures change annually). With two children at the same income level, the base obligation rises to roughly $1,200 to $1,400 per month.

These are base amounts only — they do not yet account for which parent earns more or who has custody. Once the court knows the base, it calculates each parent's share of that base by dividing their individual income by the combined income. If one parent earns $2,500 and the other earns $1,500 (combined $4,000), the first parent's share is 62.5 percent and the second parent's share is 37.5 percent.

The parent with primary custody is presumed to spend money directly on the child (housing, food, utilities), so the other parent usually pays their percentage of the base obligation. If custody is roughly equal, the higher earner pays the difference between what they owe and what the lower earner owes.

How custody time affects the amount

The more time a parent spends with the child, the less they typically owe in support. Illinois recognizes this by adjusting the obligation downward if the non-custodial parent has the child overnight more than a certain threshold — usually around 146 overnights per year, or roughly 40 percent of the time.

If the non-custodial parent has fewer than 146 overnights, they pay the full percentage of the base obligation. If they have 146 or more overnights, the court recalculates to account for their direct spending on the child during those days. The more overnights, the lower the payment obligation, because both parents are now directly spending money on the child's care.

In cases where custody is nearly equal — say, 182 overnights each — the calculation shifts entirely. The court figures out what each parent owes based on their income share, then the higher earner pays the difference to the lower earner. A parent earning $60,000 per year with 50/50 custody might owe nothing if the other parent earns similar income, or might owe several hundred dollars per month if they earn significantly more.

Income above $240,000 and other adjustments

If either parent's income exceeds $240,000 per year, the court is no longer bound by the guidelines table. Instead, the judge has discretion to set an amount above the table maximum based on the factors in the case — the child's standard of living before the separation, the child's needs, and each parent's ability to pay.

The court can also adjust the guideline amount — up or down — if certain circumstances exist. These include: one parent paying child support or spousal maintenance for other children from a different relationship; significant childcare costs or medical expenses for the child in question; either parent having substantial assets beyond income; or if the guideline amount would be unjust or inappropriate given the family's situation.

A parent can request a deviation from the guidelines by filing a motion with the court and explaining why the guideline amount is unfair. The burden is on the parent asking for the change to show why the guidelines do not fit their case.

What counts as income for child support

Income includes wages and salary, but also bonuses, commissions, self-employment earnings, rental income, interest and dividends, unemployment benefits, workers' compensation, and disability payments. It does not include means-tested public benefits like TANF (Temporary Assistance for Needy Families) or SNAP (food stamps).

If a parent is self-employed or has irregular income, the court usually averages the income over the past two or three years to smooth out fluctuations. A parent who earned $30,000 one year and $50,000 the next might be assigned an income of $40,000 for support purposes.

If a parent is intentionally underemployed — meaning they could earn more but choose not to — the court may assign them "imputed income" based on their education, work history, and job market. A parent with a college degree who is working part-time when full-time work is available might be assigned income as if they were working full-time, even if they are not actually earning that much.

When child support starts and stops

Child support begins on the date the court order is entered, or on a date the court specifies in the order. It does not automatically start from the date of separation or the date a child was born — it starts when a court or administrative body issues an order requiring it.

Support continues until the child turns 18, or until the child turns 19 if the child is still enrolled in high school full-time. Support also ends if the child is emancipated (legally declared an adult before age 18), if the child is adopted by someone other than the paying parent, or if the child dies.

If a child turns 18 but is still in high school, the paying parent must continue support through the end of that school year or until the child turns 19, whichever comes first. Once the child graduates or turns 19, the obligation ends unless the court order specifies otherwise.

How to find the current guidelines table

The Illinois Department of Healthcare and Family Services publishes the child support guidelines table each year. You can find it on the state's website or request a copy from the circuit court clerk in the county where the case is filed. The table is updated annually to account for inflation and changes in the cost of living.

If you are working with an attorney or going through the court system, the attorney or court staff can provide the current table. If you are trying to estimate what support might be, you can look up the table yourself, but remember that the actual amount will depend on your specific income, custody arrangement, and any adjustments the court makes.

Frequently Asked Questions

Does child support change if one parent loses their job?

Yes, but only if the job loss is involuntary and the parent files a motion to modify the order. A parent cannot simply stop paying because they chose to leave a job or reduce their hours. The court will look at whether the job loss was due to layoff, closure, or other circumstances beyond the parent's control, and may recalculate based on new income or imputed income.

What if the parents have equal custody and equal income?

If both parents earn the same amount and have roughly equal custody time, child support is often zero or very close to zero. Each parent is presumed to be spending money directly on the child during their custody time, so neither owes the other. However, if one parent has significantly higher income despite equal custody, the higher earner still owes support.

Can child support be ordered retroactively?

Yes. If a case goes to court and the court finds that support should have been paid before the order was entered, the court can order back support (called "arrears") going back to the date the case was filed or, in some cases, to the date of separation. The paying parent becomes responsible for the full amount owed, including any interest.

What happens if income changes after the order is entered?

Either parent can file a motion to modify the order if there has been a substantial change in circumstances — usually defined as a 20 percent or greater change in either parent's income. The court will recalculate based on the new income and may increase, decrease, or leave the amount the same depending on how both parents' incomes have changed.

Is child support tax-deductible?

No. The parent paying child support cannot deduct it from their federal income taxes, and the parent receiving it does not report it as income for tax purposes. This is different from spousal maintenance (alimony), which may have different tax treatment depending on when the order was entered.