I get some version of this call regularly: "My divorce was finalized three years ago, but my situation has completely changed. Can I fix the order?" Sometimes the answer is yes. Sometimes it isn't, at least not yet. The difference usually comes down to one legal standard that surprises people the first time they hear it.
The Standard: Substantial Change in Circumstances
Courts don't reopen custody, support, or parenting orders just because one parent is unhappy with how things turned out, or wishes they'd negotiated differently the first time. Both Missouri and Illinois require a substantial, often unanticipated, change in circumstances since the original order before a judge will consider modifying it. That standard exists on purpose. Without it, every disagreement between former spouses could turn into another round of litigation, and kids in particular need stability, not a court order that's constantly up for renegotiation.
What Usually Qualifies
Common triggers I see include a significant, involuntary job loss or pay cut, a parent relocating for work or family, a child's needs changing substantially, new medical, educational, or safety concerns, or one parent remarrying in a way that materially changes the household. Cost-of-living increases alone typically aren't enough on their own for a support modification, but combined with an income change, they often are. Every court weighs these facts differently, which is exactly why the specifics of your situation matter more than any general rule of thumb.
What Usually Doesn't
Simply being unhappy with the original agreement isn't grounds for modification, even if you've since decided you negotiated a bad deal. A voluntary decision, like quitting a job to take a lower-paying one you'd prefer, generally won't support lowering a support obligation either. Courts look closely at whether a change was genuinely outside a parent's control, because the substantial-change standard is meant to catch real shifts in circumstances, not buyer's remorse.
Relocation Cases Get Extra Scrutiny
If the parent with the majority of parenting time wants to move, especially out of state or far enough to disrupt the existing schedule, both Missouri and Illinois treat that as its own category of modification, with specific notice requirements and factors the court has to consider. A job opportunity or a new relationship in another city doesn't automatically justify uprooting a child's school, friends, and relationship with the other parent. Courts weigh the reason for the move, the impact on the child, and whether a revised parenting schedule could preserve the relationship with the parent staying behind. These cases tend to be more contested than a typical modification, and they benefit from being handled carefully and early, before a move is already underway.
Custody and Parenting Time vs. Support
Modifying custody or a parenting schedule and modifying support are technically separate processes, though they often get requested together when a family's whole situation has shifted. Courts tend to apply a somewhat higher bar to changing established custody or parenting-time arrangements, since disrupting a child's routine has its own costs, separate from whatever prompted the request. Support modifications, by contrast, often turn more directly on the numbers: what each parent earns now compared to what the original order assumed.
The Process
A modification starts with filing a formal motion, supported by evidence of the changed circumstances, pay stubs, medical records, documentation of a move, whatever's relevant to your situation. From there, many modifications resolve through negotiation between the parties once the facts are laid out clearly. When they don't, the matter proceeds to a hearing, where a judge decides based on the evidence presented. Once the court signs off, the new order replaces the original, and both parties are bound by the updated terms going forward.
One Important Distinction: Modification vs. Enforcement
If your ex simply isn't following the existing order, that's an enforcement problem, not a modification problem, and it's handled differently. Don't confuse the two. If support isn't being paid or parenting time isn't being honored, the order itself is presumably still fine; what's needed is a path to enforce it, which is a different conversation than asking a court to change the terms.
If your circumstances have genuinely shifted since your divorce, it's worth having an honest conversation about whether you meet the standard before you file anything. That assessment upfront saves most people time, money, and a motion that was never going to succeed.