Illinois Child Support Calculator
Calculate estimated child support using Illinois' official guidelines
About Illinois' Guidelines
Income Shares Model (changed from percentage in 2017)
Note: Uses net income, includes detailed adjustments for shared parenting
Key Information
- •Model: Income Shares
- •Last Updated: January 15, 2024
Common Deviation Factors
Monthly Income
Children & Custody
Additional Monthly Expenses
Estimates only — not legal advice. Consult a Illinois family law attorney for official calculations.
Official Illinois Court Forms
Download official court forms from the Illinois judiciary website. These are free, legally valid forms for your family court case.
Child Support Forms
Official petitions & worksheets
Modification Forms
Request changes to orders
Financial Disclosure
Income & expense statements
These links go to official Illinois court websites. Forms are free and provided by the state judiciary.
Illinois Child Support Guidelines
Illinois uses the Illinois Income Shares Guidelines (750 ILCS 5/505) to determine child support obligations. Under the Income Shares model, both parents' incomes are combined to estimate what the family would have spent on the child if the household were intact. The obligation is then divided proportionally based on each parent's contribution to combined net income.
Illinois has several distinctive features in its child support system. Illinois switched from percentage-of-income to income shares in 2017 — the biggest recent model change in the US. Illinois requires 146+ overnights (40%) to trigger shared parenting — one of the highest thresholds in the country. The state uses standardized "net income" which is gross minus taxes, Social Security, Medicare, mandatory retirement, and union dues.
Illinois bases calculations on net income — meaning income after mandatory deductions like taxes, Social Security, and Medicare. This gives a more accurate picture of each parent's take-home pay. The self-support reserve in Illinois is $1,287/month, ensuring the paying parent retains enough income to cover basic living expenses.
How Illinois Calculates Child Support
Illinois follows a 7-step process under the Illinois Income Shares Guidelines (750 ILCS 5/505):
- 1
Determine each parent's gross monthly income
- 2
Convert to standardized net income by deducting taxes (using standardized tax amount), Social Security, Medicare
- 3
Also deduct: maintenance (alimony) paid, child support for prior children, multi-family adjustment
- 4
Combine net incomes and find basic support obligation from the Illinois Schedule
- 5
Each parent's share is their percentage of combined net income
- 6
If 146+ overnights: multiply basic obligation by 1.5, calculate each parent's share, and offset
- 7
Add shares of childcare and children's health insurance premiums
Income Thresholds & Key Numbers in Illinois
Self-Support Reserve
$1,287/mo
Shared Custody Threshold
146 nights/yr
40% of overnights
Income Basis
net
Sample Obligation Schedule
| Combined Monthly Income | 1 Child | 2 Children | 3 Children |
|---|---|---|---|
| $1,500 | $247 | $359 | $430 |
| $3,000 | $447 | $651 | $789 |
| $5,000 | $653 | $958 | $1,163 |
| $8,000 | $905 | $1,335 | $1,622 |
| $12,000 | $1,175 | $1,738 | $2,115 |
| $20,000 | $1,578 | $2,335 | $2,845 |
* Simplified schedule. Actual amounts may vary based on additional factors.
Custody Time Adjustments in Illinois
Illinois recognizes "Shared Parenting (146+ Overnights)" when the non-custodial parent has the children for at least 146 overnights per year (approximately 40% of the time). When this threshold is met, the standard child support formula is adjusted to reflect the increased direct expenses borne by both parents.
Under Illinois' Income Shares approach, the shared parenting adjustment typically calculates each parent's obligation based on their income share, then applies a credit or cross-calculation that accounts for the time each parent directly supports the child. The more overnights the non-custodial parent has, the greater the reduction in their payment — but the adjustment is not dollar-for-dollar because fixed costs like housing don't decrease when the child is away.
Below 146 overnights, Illinois generally treats the arrangement as a sole custody situation with standard visitation, and no custody time adjustment is applied to the child support calculation.
Frequently Asked Questions About Illinois Child Support
When did Illinois switch to income shares?
What is the 146-night rule in Illinois?
How does Illinois calculate net income?
How to Reduce Child Support Costs in Illinois
While child support is determined by Illinois' guidelines, there are legitimate ways to ensure your obligation is calculated fairly.
Increase Parenting Time
In Illinois, more overnights with your children can reduce your support obligation. Document actual time spent and request a formal custody modification if needed.
Ensure Accurate Income Reporting
Both parents' incomes must be reported accurately. Verify that bonuses, overtime, and variable income are averaged correctly over the appropriate period.
Claim All Allowable Deductions
Illinois allows deductions for items like mandatory retirement contributions, union dues, and health insurance premiums. Make sure all qualifying deductions are included.
Request a Modification When Eligible
If your income has decreased by 15-25% or more, you may qualify for a modification. File promptly — changes are typically not retroactive before the filing date.
Account for Other Children
If you have other children you're legally obligated to support, this can be factored into the calculation as a deduction in most states.
Review Healthcare & Childcare Costs
Ensure shared expenses like health insurance and childcare are divided proportionally. If costs have changed, update the court.
Key Facts About Child Support in Illinois
Calculation Model
Income Shares
Guidelines Source
State Statute
Review Frequency
Every 4 Years
Last Updated
January 15, 2024
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