How to modify child support or spousal maintenance in Illinois

Sources last checked: 3 November 2026. Information only, not legal advice. The Cusp is not a law firm.

Illinois divorce kit How child support is calculated Alimony in Illinois Legal aid in Illinois

The short version

In Illinois, one statute, section 510 of the Illinois Marriage and Dissolution of Marriage Act, governs changes to both child support and maintenance. You start by filing a motion or petition to modify. A change reaches back only to the date the other side was given notice of your filing, so the timing of that notice matters (details below). For child support only, the Illinois Department of Healthcare and Family Services (HFS) Child Support Services will also review an order for free if you have an open case with it. We did not find an official statewide standardized court form for a motion to modify support or maintenance (see “What we could not confirm” below).

What the motion can ask for

Child support: the order may be modified on “a substantial change in circumstances”. Separately, without showing a change, on “an inconsistency of at least 20%, but no less than $10 per month” between the existing order and the guideline amount, or on a need to provide for the child’s health care needs through health insurance or other means. That second route has limits in the statute (details below).
Spousal maintenance: an order may be modified or terminated “only upon a showing of a substantial change in circumstances”. Section 504 confirms that a proceeding to modify a maintenance order is one in which the court may make a maintenance award.
Property division: property disposition “may not be revoked or modified” unless the court finds conditions that justify reopening the judgment. This is not an ordinary modification.

What the statutes say

Wording below is a plain-language summary of the Illinois Compiled Statutes as we read them on 3 November 2026, with short quotations.

How far back a change reaches, 750 ILCS 5/510(a): support or maintenance may be modified “only as to installments accruing subsequent to due notice by the moving party” of the filing of the motion. The subsection opens with exceptions that point to section 502(f) and section 505.2, which we did not read.
Child support, 510(a)(1): “a substantial change in circumstances”. Future events are not counted against you as foreseeable unless the order or the incorporated agreement expressly specified them.
Child support without a change, 510(a)(2)(A): the 20 percent and $10 route is skipped if the gap exists only because the existing order deviated from the guidelines and the reason for that deviation has not changed. The statute applies it only where a party receives child support enforcement services from HFS, and only when “at least 36 months have elapsed” since the order was entered or last modified.
Child support and health care, 510(a)(2)(B): a modification may rest on a need to provide for the child’s health care through insurance or other means.
Spousal maintenance, 510(a-5) and (c-5): the court must consider “the applicable factors set forth in subsection (a) of Section 504” and a further list that includes changes in employment, the recipient’s efforts to become self-supporting, and changes in each party’s income. In an adjudicated case it must “make specific factual findings as to the reason for the modification”.
Maintenance that ends by itself, 510(c): unless the parties agreed otherwise in writing or the court approved otherwise, the duty to pay future maintenance ends on either party’s death, on the recipient’s remarriage, or if the recipient “cohabits with another person on a resident, continuing conjugal basis”. The payor’s obligation “terminates by operation of law” on the date of remarriage or the date the court finds cohabitation began, and the payor is entitled to reimbursement from that date.
Indefinite maintenance, 504(b-4.5)(2): “Indefinite maintenance shall continue until modification or termination under Section 510”. For maintenance ordered before 2019, 504(b-4) says payments “continue to retain the same tax treatment” after a later modification unless both parties expressly agree otherwise in the modification order.
Child support ends by itself, 510(d): unless the judgment says otherwise, support ends on the child’s emancipation, or, if the child is 18 and still in high school, on graduation or the 19th birthday, whichever is earlier.
Enforcement keeps running, 510(f): a petition to modify or terminate child support or parenting time “shall not delay any child support enforcement litigation” for the person owed support.
Coming 1 January 2027: a later version of section 510, shown on the same page with the source note P.A. 104-733, eff. 1-1-27, adds a child support ground for a parent who will be “incarcerated for more than 180 consecutive days” (or is released from such a stretch). Under it, support can drop to $0.00 by operation of law if a notice of incarceration is filed and no written objection comes “within 45 days of the effective date of the notice of incarceration”. It is not yet in force on our check date.

Using Child Support Services instead

The HFS page “Request a Modification” says you can petition the court yourself or use Child Support Services (CSS) to review your case at no charge. Points it makes:

“You must have a case with CSS for our assistance in completing a modification”. HFS says a case can be opened at any time.
“Guidelines require CSS cases be reviewed every three years”. On the amount it says “As a rule, a 20% increase or decrease is required for a change”. The statute above states the test with a $10 floor, so read the statute for the exact test.
The order can go up or down after the review. HFS says the order may not be what you expected.
“There is no charge for making a modification request”. The CSS attorney does not represent either parent.
If CSS denies the request, “you can still go to court on your own” for a judge to decide.
HFS says “we cannot address visitation and custody issues”. It suggests a private attorney for those.
To request a review: HFS lists an online modification form, a phone line (888.245.1938), and a fillable email route using an Affidavit of Income and Expenses and a Disclosure Statement on Legal Representation. HFS also lists changes it says should prompt a request, such as a job loss, an income change, a change in custody or visitation, or disability, and says you will need proof.

HFS covers child support only. The pages we read do not mention spousal maintenance.

Court forms

The Illinois Supreme Court Commission on Access to Justice approves statewide standardized forms, and the Illinois Courts site says “All Illinois Courts must accept these forms”. What we found on those pages:

Divorce, Child Support, and Maintenance suite: its child support and maintenance group lists How to Get an Order for Support, Order for Support, Support Information Sheet (each approved 09/2025), Income Withholding for Support (a federal form), and a Letter to Employer About Income Withholding for Support. These are titled for getting an order, not for changing one. None is titled as a modification.
Financial Affidavit (Family & Divorce Cases): approved 06/2025, with an Additional My Child Support attachment. It is part of the family suite. We did not confirm whether a given court asks for it with a modification.
Motions and Notice: the only form listed is a Motion to Continue (Reschedule) or Extend Time.
Fee waiver: the statewide list includes a Fee Waiver for Civil Cases. We did not read its terms or revision date.

Many circuits publish their own forms. We did not review any of them.

Before you file

Court staff cannot give legal advice. See legal aid in Illinois for free or low-cost help, or the Illinois divorce kit for the wider process.
Because a change reaches back only to notice of the filing, ask the clerk how to file and give notice in your court as soon as you decide to move.
Child support amounts follow the state guidelines. See how child support is calculated in Illinois and alimony in Illinois.
This page does not state a court filing fee, because no official source we read gives one for a modification.

What we could not confirm

An official statewide form for a motion or petition to modify. The statewide standardized forms we read include none for modifying child support or maintenance. Your circuit clerk may have its own. We did not search every circuit.
Filing fees and service fees. No official source we read states an amount for a modification.
How to give “due notice”. Section 510(a) uses that phrase. We did not read the Illinois Supreme Court Rules or the Code of Civil Procedure rules on notice and service, or any circuit rule on setting the motion for hearing.
Which court and which county. We did not confirm venue rules, for example after a move.
Other statute sections. We did not read section 502(f) (agreements that bar modification), section 505 (the guidelines), section 505.2, or the rules on changing parenting time.
Administrative rules and agency detail. We did not search the Illinois Administrative Code or read HFS rules, the HFS online form, or its processing times.
Form revision dates. We read approval dates on the Illinois Courts list for the forms named above. We did not open the PDFs, and we did not read dates for the HFS forms.

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