In re Marriage of Durdov, 206 N.E.3d 933

Veronica and Eric Durdov divorced in 2016; they have two minor children. Their dissolution incorporated a Marital Settlement Agreement (MSA) and Joint Parenting Agreement (JPA).
The MSA set child support at $2,776/month (28% of Eric’s net income based on $211,000) and included a "true-up" requiring Eric to pay 28% of any additional net income (bonuses, commissions, etc.).
The MSA imputed income to Veronica for maintenance: $20,000/year for years 1–4 and $65,000 in year 5; child support did not expressly impute income to her.
After the divorce Veronica went from nominal substitute-teacher income (~$1,500 in 2016) to full-time employment at Northwestern, eventually earning ~$58,380/year. Eric later obtained a new job with a signing bonus and salary increase to about $247,000–$252,000.
Eric filed to reduce his child support obligation in Sept. 2017 (after Veronica’s promotion and a statutory shift to an income-shares guideline). The trial court found a "substantial change in income" for both parties, applied the income-shares approach, and reduced child support to $1,567/month.
The appellate court reversed, holding both parties’ income increases were contemplated by the settlement (Veronica via imputed income and a career-outplacement order; Eric via the true-up), so no substantial change in circumstances justified modification.

Issue	Plaintiff's Argument (Veronica)	Defendant's Argument (Eric)	Held
Whether Veronica’s post-divorce increase in income is a "substantial change in circumstances" warranting downward modification of Eric’s child support	The parties contemplated her obtaining gainful employment (career counseling order and imputed incomes in the MSA); therefore the increase was not a substantial change	Her increase in earnings after divorce is a quintessential substantial change that justifies lowering Eric’s support obligation	Reversed: appellate court held the MSA (career counseling order and imputed-income schedule) shows the parties contemplated her increased earnings, so no substantial change
Whether Eric’s increased earnings constitute a "substantial change in circumstances"	Eric’s salary increase was contemplated by the MSA’s true-up clause requiring 28% of additional net income; thus it cannot alone justify modification	The increase in Eric’s income supports recalculation under the new statute and justifies a reduction	Reversed: appellate court held the true-up provision shows the parties anticipated increased earnings, so Eric’s raise is not a substantial change

Blum v. Koster, 235 Ill. 2d 21 (2009) (abuse-of-discretion standard for child-support modification)
In re Marriage of Maczko, 263 Ill. App. 3d 991 (1992) (both parents share financial responsibility for minor children)
People v. Armstrong, 346 Ill. App. 3d 818 (2004) (small percentage salary increases do not constitute a substantial change in circumstances)
In re Marriage of Butler, 106 Ill. App. 3d 831 (1982) (minor earnings increases are insufficient to show a substantial change)