Can I Make a Big Purchase During an Illinois Divorce?
Parents almost never agree on what child support should be until they see how it is actually calculated. Illinois does not leave it to a judge's gut feeling, or to a flat percentage of one parent's paycheck. It runs both parents' income through a formula, and understanding that formula tells you far more than any rumor from a friend's divorce ever will.
The Income Shares Model in Plain Terms
Illinois calculates child support under 750 ILCS 5/505 using what is called the income shares model. The idea behind it is simple even though the math has steps. The law tries to estimate what the parents would have spent on the child if the household had stayed together, based on both parents' combined income, and then splits that number between the parents in proportion to what each one earns. This replaced the older percentage of income model back in 2017, and most parents who remember the old system are surprised at how differently the numbers can land under the current one.
The Four Steps
In practice, the calculation follows four steps.
- Each parent's monthly net income is calculated, using the state's Gross to Net Income Conversion Table rather than whatever number shows up on a pay stub.
- Both parents' net incomes are added together to get a combined monthly net income.
- That combined number is looked up on the Illinois Schedule of Basic Child Support Obligations, published by the Department of Healthcare and Family Services, to find the basic support obligation for the number of children involved.
- That basic obligation is split between the parents in proportion to each parent's share of the combined income. A parent earning 60 percent of the combined income generally owes 60 percent of the basic obligation.
Net income for this purpose is not simply take home pay. It accounts for taxes, certain mandatory deductions, and other adjustments set out in the statute, which is one reason a self calculated number based on a pay stub often does not match what the court's schedule actually produces.
Shared Parenting Changes the Math
The calculation above assumes one parent has the child most of the time. When parenting time is closer to equal, the math shifts. Under the shared physical care provisions of Section 505, if each parent has the child for 146 or more overnights per year, the basic support obligation is multiplied by 1.5 to reflect that both households are covering the child's day to day costs. Each parent's share of that adjusted obligation is then calculated based on income, and then reduced further based on the percentage of time the child spends with the other parent. The two resulting numbers are offset against each other, and the parent who owes more pays the difference. It is more complicated than the standard calculation, and it is exactly the kind of math worth double checking with your attorney rather than estimating on your own.
When a Court Can Deviate
The guideline number is not absolute. A judge can order an amount different from what the formula produces, but only after finding that following the guidelines would be inappropriate given the child's best interests, and only after weighing factors like the child's financial needs, each parent's resources, the standard of living the child would have had if the family had stayed together, and the child's physical, emotional, and educational needs. If a court deviates, it has to say so on the record, state what the guideline amount would have been, and explain why it went a different direction. This is not a loophole either parent can use casually. The parent asking for a deviation carries the burden of showing why it is warranted.
What Gets Added On
The basic obligation is not always the final number. A court has discretion to add on top of it for expenses like reasonable childcare costs tied to a parent's work or job search, and the court must also address the child's health insurance, ordering one or both parents to carry coverage and to split any related premium or out of pocket costs. These add-ons get allocated between the parents, usually in proportion to income, on top of the base child support figure.
The HFS Estimator
The Illinois Department of Healthcare and Family Services publishes a free online Child Support Estimator that walks through this calculation using current income tables and the current schedule of obligations. It is a useful starting point to get a rough number before a case is even filed, but the state itself is clear that the estimator is for general guidance only and the actual amount a court or the Department orders may come out differently once specific facts, like actual overnights or documented childcare costs, are factored in.
Modifying Support Later
A child support order is not permanent. Under 750 ILCS 5/510, a parent can ask the court to modify support if there has been a substantial change in circumstances, such as a job loss, a significant raise, or a real change in the child's needs. Separately, a parent does not even need to show a substantial change if the current order is off by at least 20 percent from what the guidelines would produce today, which gives either parent a path to revisit a stale order as incomes shift over time. Neither path is automatic. Someone has to file the motion and put real numbers in front of the court.
When to Get Help
Child support numbers look simple on a calculator and get complicated fast once real income, real overnights, and real expenses enter the picture. Jeff McCarthy handles child support cases, both new orders and modifications, for families throughout Lockport, Joliet, and Will County. Call (815) 838-5297 to find out what the numbers actually look like in your case.
Related: Child Support · Illinois family law FAQ
Questions People Ask
How is child support calculated in Illinois?
Illinois uses the income shares model under 750 ILCS 5/505. Each parent's net monthly income is calculated using the state's conversion table, the two incomes are combined and looked up on the Illinois Schedule of Basic Child Support Obligations, and that basic obligation is split between the parents based on each one's share of the combined income. A parent earning 60 percent of combined income generally owes 60 percent of the basic obligation.
Does shared parenting time change the child support calculation in Illinois?
Yes. If each parent has the child for 146 or more overnights per year, the basic support obligation is multiplied by 1.5 to reflect that both households cover day to day costs. Each parent's income-based share of that adjusted obligation is then reduced based on the percentage of time the child spends with the other parent, and the two numbers are offset so the parent who owes more pays the difference.
Can I get my Illinois child support order changed later?
Yes. Under 750 ILCS 5/510, a parent can ask the court to modify support if there has been a substantial change in circumstances, such as a job loss or a significant raise. A parent can also seek modification without showing a substantial change if the current order is off by at least 20 percent from what the guidelines would produce today. Either path requires filing a motion with real numbers.
