Illinois child support for one child is calculated by a formula, not a flat amount

Illinois does not have a set dollar amount for child support. Instead, the state uses a income shares model, which means the amount depends on how much both parents earn. The court takes the combined income of both parents, applies a percentage based on the number of children, and divides the obligation between them based on each parent's share of the total income.

For one child, the percentage is 20% of the combined net income of both parents. If you earn $50,000 per year and the other parent earns $30,000, your combined income is $80,000. Twenty percent of that is $16,000 per year, or about $1,333 per month. How that $1,333 is split between you depends on who has custody and each parent's income proportion.

The actual payment you make or receive can range from under $100 per month to over $3,000 per month, depending on both parents' incomes and custody arrangement. There is no minimum or maximum set by law for a single child, though courts can deviate from the formula if they find it unjust.

Key Takeaways

  • Illinois calculates child support as 20% of combined parental net income for one child, divided between parents based on their individual income shares.
  • Net income includes wages, salary, and self-employment income, minus taxes, union dues, and certain court-ordered support obligations.
  • The parent with primary custody usually receives the payment from the other parent, but the amount is based on both parents' incomes regardless of custody split.
  • Either parent can request a modification if income changes by 10% or more, or if there is a substantial and continuing change in circumstances.
  • The court order specifies the exact monthly amount and payment method, and enforcement goes through the Illinois State Disbursement Unit if the payer does not pay directly.

How Illinois calculates the 20% for one child

The calculation starts with net income, not gross income. Net income means what you actually take home after taxes, Social Security, Medicare, union dues, and certain other deductions. Self-employment income is reduced by a percentage to account for self-employment taxes. Bonuses, overtime, rental income, and investment income all count as income.

Once both parents' net incomes are added together, the court multiplies that total by 0.20 (20%). That number is the total child support obligation. If one parent earns 60% of the combined income and the other earns 40%, the parent earning 60% typically pays 60% of the total obligation.

The parent with primary custody (the one the child lives with most of the time) usually receives the payment. However, if custody is split 50/50, both parents still have an obligation based on their income share, and the higher-earning parent typically pays the lower-earning parent the difference.

What counts as income and what does not

Income includes W-2 wages, salary, self-employment earnings, bonuses, overtime, commissions, rental income, interest and dividend income, and income from a business or partnership. It also includes unemployment benefits, workers' compensation, and certain disability payments.

Income does not include child support or spousal support you receive from another relationship, TANF (Temporary Assistance for Needy Families), SNAP (food stamps), SSI (Supplemental Security Income), or need-based public assistance. Gifts and loans do not count as income.

If you are self-employed or have irregular income, the court may average your income over the past two years. If you recently changed jobs or had a major income change, bring documentation of both the old and new income to court.

When the court can order a different amount

The 20% formula is the starting point, but Illinois law allows courts to deviate if applying the formula would be unjust or inappropriate. Courts consider factors like the financial resources of each parent, the standard of living the child would have had if the marriage had not ended, the non-monetary contributions each parent makes to the care of the child, and the tax consequences to each parent.

A court might order less than 20% if one parent has very high income and paying the full percentage would be excessive, or if the parent paying has other children from different relationships. A court might order more than 20% if the paying parent has significant assets or if the child has special needs.

The court must state in writing why it is deviating from the formula and by how much. If you think the amount ordered is unfair, you can appeal, but you must show the court abused its discretion — simply disagreeing with the math is not enough.

How to modify child support if income changes

Either parent can ask the court to change the child support amount if there has been a substantial and continuing change in circumstances. A change in income of 10% or more is considered substantial. You do not have to wait for a specific time period — you can file for modification whenever the change occurs.

To start a modification, you file a petition with the circuit court in the county where the original order was entered. You will need to provide recent pay stubs, tax returns, and documentation of the income change. The other parent gets a copy and can respond. If you both agree on the new amount, you can submit a written agreement to the judge for approval. If you disagree, the court holds a hearing.

Child support modifications are effective from the date you file the petition, not from the date the new order is signed. If you wait a long time to file after your income changes, you cannot collect back support for the months you waited.

How payment is handled and enforced

The court order specifies how much to pay, when to pay it, and to whom. Most orders require payment to go through the Illinois State Disbursement Unit (SDU), a centralized payment processing system. You send your payment to the SDU, and they forward it to the other parent. This creates an official record of all payments.

Some orders allow direct payment between parents, but the SDU route is safer because it documents that you paid. If you pay cash or by personal check directly to the other parent and they later claim you did not pay, you have no proof.

If you fall behind on payments, the other parent can file for enforcement. The court can garnish your wages, intercept your tax refund, suspend your driver's license, or hold you in contempt of court. If you cannot pay because of job loss or hardship, you can ask the court to modify the amount, but you must file the petition — simply not paying does not stop the debt from growing.

Income limits and special situations

Illinois has no income cap for the child support formula. If combined parental income exceeds $240,000 per year, the court can apply the 20% to the first $240,000 and then decide what to do with income above that amount. The court has discretion to apply the percentage to all income, cap it, or use a different method.

If one parent is incarcerated, unemployed, or unable to work, the court may impute income — meaning it assigns an income level based on what the parent could earn. The court looks at the parent's age, education, work history, and job market. It does not automatically assume zero income just because the parent is not currently working.

If a parent is a full-time student or caring for a young child, the court may consider that when setting income, but it does not automatically reduce the obligation. You have to present evidence and ask the court to consider it.

Frequently Asked Questions

Can child support change if the other parent loses their job?

Yes, but only if they file for modification and show the job loss is not voluntary. If someone quits their job to avoid paying support, the court will not reduce the amount. If they were laid off or fired through no fault of their own, they can file a petition and the court will recalculate based on their new income or imputed income.

What if I have another child with a different partner after the order is entered?

A subsequent child does not automatically reduce your obligation to the first child. However, you can file for modification and ask the court to consider the new child. The court may reduce your obligation, but it will not eliminate it. The first child's support is usually prioritized.

Does child support end at age 18 in Illinois?

Child support ends when the child turns 18, unless the child is still in high school, in which case it continues until graduation or age 19, whichever comes first. If the child has a disability, support can continue beyond 18 if the court orders it.

Can I get child support reduced if I pay for health insurance or daycare?

Health insurance and daycare costs are factored into the calculation separately from the base child support amount. The court adds these costs on top of the 20% obligation, and both parents share them based on their income proportion. You do not reduce the base amount; instead, you pay your share of these add-on costs.

What happens if the other parent moves out of state?

Illinois can still enforce the order through the Uniform Interstate Family Support Act (UIFSA). You can file for enforcement in Illinois even if the other parent lives in another state. The other state's court will recognize the Illinois order and can enforce it through wage garnishment or other means.