Illinois Child Support Calculator
Calculate Illinois guideline child support with built-in maintenance sequencing, shared parenting, and add-on reimbursements.
Run Your Income Shares Scenario
Enter monthly income, allowable deductions, parenting schedule, and add-on expenses. We model maintenance, compute adjusted net incomes, and apply the shared care cross-credit when applicable.
Which best describes you?
Illinois Guideline Support
750 ILCS 5/504 & 5/505 Income Shares • Monthly amounts
Need more information
Enter at least one child plus monthly gross income for both parents.
Inside the Illinois Income Shares Model
Illinois calculates a Basic Child Support Obligation (BCSO) from the combined adjusted net income and the number of children. Maintenance must be determined first, then net incomes are adjusted before finding the BCSO and allocating parenting-time credits. The payor’s share of add-on costs is reimbursed through the monthly transfer amount.
Workflow Highlights
- Maintenance-first sequencing with 40% cap validation.
- Shared care cross-credit triggers at 146 nights per parent.
- Add-on reimbursements align with each parent’s income share.
Best Practices
- Verify the BCSO against the HFS table before filing.
- Document add-on expenses and who pays them for clean reimbursement math.
- Stress-test shared parenting scenarios to prepare for deviations.
Step-by-Step Calculation
- Collect monthly gross income. Enter all recurring income plus allowable deductions to approximate net income under 750 ILCS 5/505(a)(3).
- Determine maintenance. Apply the 33⅓% – 25% formula, 40% cap, and guideline applicability test. Adjust each parent’s net income accordingly.
- Compute the BCSO. Use the combined adjusted net income and number of children to find the Basic Child Support Obligation. (Confirm against the HFS table for court filings.)
- Assess parenting time. If both parents have ≥146 nights, apply the 1.5 multiplier and cross-credit to balance income and parenting time.
- Allocate add-ons. Prorate childcare, insurance, and extraordinary expenses and adjust the transfer to reimburse the parent who pays more than their share.
Shared Care Planning
Test different parenting-time splits to see how the cross-credit changes the payment and whether deviations are warranted.
Maintenance Linkage
Maintenance directly alters the child support calculation. Keep both outputs together for negotiations.
Deviation Ready
Use the full output to support deviations under 750 ILCS 5/505(a)(2) when the guideline appears unjust.
Frequently Asked Questions
How much child support will I pay in Illinois?
Illinois child support amounts depend on your combined monthly net income, number of children, and parenting time. Use our calculator above to get an estimate based on the Income Shares model under 750 ILCS 5/505.
What if I have 50/50 custody in Illinois?
When both parents have at least 146 overnights per year, Illinois applies a "shared care" adjustment. The basic support obligation is increased by 50% and cross-credited based on each parent's income share and parenting time.
How does spousal maintenance affect child support?
Illinois requires calculating maintenance first. Any maintenance payments adjust each parent's net income before determining the child support obligation under the Income Shares model.
Can I modify my Illinois child support order?
Yes, if there's been a substantial change in circumstances or it's been 3+ years since your last order. Use this calculator to estimate what your new payment might be before filing a modification petition.
Are childcare and medical expenses included?
Childcare, children's health insurance premiums, and extraordinary medical expenses are allocated between parents based on their income shares and added to or subtracted from the basic support amount.
Stay Synced with Illinois Guideline Updates
When the HFS schedule or Poverty Guideline thresholds change, we update the engine so your estimates track with courtroom expectations. Always confirm the BCSO from the official table before filing.
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