A child support modification in Missouri changes an existing support order when a parent’s financial or custodial situation has shifted enough to make the current amount unreasonable. You can request one through the Family Support Division or by filing a Motion to Modify in the circuit court that issued your original order, and Missouri law presumes modification is warranted when a fresh calculation produces an amount at least 20% higher or lower than what you’re paying now.1Missouri Revisor of Statutes. Missouri Code 452.370 – Modification of Judgment as to Maintenance or Support The new amount applies only to payments coming due after the other parent has been formally served, so the sooner you file, the less money you leave on the table.
What Counts as a Qualifying Change
Missouri does not modify support for minor or temporary bumps in the road. The parent asking for the change has to show circumstances have shifted so significantly, and will stay that way, that the existing order no longer fits.1Missouri Revisor of Statutes. Missouri Code 452.370 – Modification of Judgment as to Maintenance or Support A permanent disability, a major promotion, a layoff followed by months of unsuccessful searching, or a child developing serious medical needs would qualify. One slow month at work would not.
The statute gives you a concrete benchmark. If running the numbers through Missouri’s child support formula produces an amount at least 20% higher or lower than the current order, that gap alone creates a legal presumption that the existing order is unreasonable.1Missouri Revisor of Statutes. Missouri Code 452.370 – Modification of Judgment as to Maintenance or Support The other parent can still argue against modifying, but the 20% difference shifts the burden in your favor.
The “continuing” part matters more than people expect. Courts want durability. If you were laid off last month and started a comparable job this week, the change was real but not continuing. If you’ve been out of work for six months despite a genuine search, the change looks permanent and a court is far more likely to act.
There’s also a separate track through the Family Support Division: after three years from the most recent order, either parent can request an FSD review even without meeting the 20% threshold.2Missouri Department of Social Services. Missouri Child Support – Changing Your Support Order
Common Reasons Parents File
The most frequent trigger is a meaningful income change on either side. The paying parent may have lost a job, switched careers, or become disabled. The receiving parent may have started earning significantly more. Either can push the recalculated number past 20%.
Custody shifts drive modifications too. If your child starts spending substantially more overnight time with you, the formula accounts for that and the obligation can drop. If the other parent takes on more parenting time, the number moves the other way.
Rising child-specific costs are another common ground. A new medical diagnosis with ongoing treatment, a jump in health insurance premiums, or the start of necessary childcare expenses can all raise the total obligation when plugged into the formula.
Does a New Spouse’s Income Count
In most cases, no. Missouri’s formula uses the gross incomes of the biological or adoptive parents, not a new partner’s earnings, and a new spouse is not required to support someone else’s child. That said, if you claim inability to pay, the court can look at your broader household picture. The statute specifically directs courts to consider expenses that are or should be shared by a spouse or other person you live with.1Missouri Revisor of Statutes. Missouri Code 452.370 – Modification of Judgment as to Maintenance or Support If remarriage has cut your housing costs in half, a judge can factor that in.
Voluntary Underemployment
This is where many modification attempts collapse. If a parent quits a well-paying job or takes a lower-paying position on purpose, the court is not required to accept the reduced income at face value. Missouri courts can impute income, meaning they calculate support based on what you could earn rather than what you currently earn. The imputed figure must be supported by evidence of your actual earning capacity, including education, work history, and job market conditions. Even without proof you were dodging support, a judge can impute higher income when the evidence shows you’re capable of earning more.
How the New Amount Gets Calculated
Every Missouri child support calculation runs through a standardized worksheet called Form 14. Both parents complete it, and the result is the “presumed” amount a judge will order unless someone shows it would be unjust in their specific situation.3Missouri Courts. Form 14 Child Support Amount Calculation Worksheet
The worksheet combines both parents’ adjusted monthly gross income and pulls the corresponding figure from the Schedule of Basic Child Support Obligations, which estimates typical spending on children at that income level. Each parent’s share of the basic obligation is proportional to their share of the combined income.4Missouri Courts. Directions, Comments for Use and Examples for Form 14
From there, Form 14 layers in additional costs: work-related childcare, health insurance premiums for the child, uninsured extraordinary medical costs, and any other court-ordered extraordinary expenses. The paying parent receives a credit for overnight time the child spends in their care, reducing the final number to reflect expenses already covered during those overnights.3Missouri Courts. Form 14 Child Support Amount Calculation Worksheet Judges follow the resulting number in the vast majority of cases. Deviating requires specific evidence the presumed amount is unjust or inappropriate.
Documents to Gather Before You File
Accurate paperwork separates a clean modification from one bogged down in disputes over basic facts. Start with income documentation: recent pay stubs covering at least several months so the court can see a reliable average, plus federal and state tax returns from the past two years. If you earn commissions, bonuses, or freelance income, those returns matter especially because they capture money that doesn’t appear on every pay stub.
You also need documentation of the child’s costs. Collect statements showing the monthly premium for your child’s health insurance, receipts or invoices for childcare, and billing records for any extraordinary medical expenses. Those figures feed directly into Form 14, and missing or inaccurate numbers distort the calculation.
Form 14 is available through the Missouri Courts website. Filling it out requires both parents’ financial information and the child’s specific expense data. Discrepancies between what you report and what your documents show can delay the process or give the other side ammunition. Get it right the first time.
The Two Ways to Request a Modification
Missouri gives you two routes: an administrative review through the Family Support Division, or a judicial motion filed in circuit court.
Through the Family Support Division
If the state already manages your case, for instance because payments run through income withholding or you receive public assistance, you can request a review directly from FSD by written request or fax.2Missouri Department of Social Services. Missouri Child Support – Changing Your Support Order FSD evaluates your financial information, and if the case qualifies, issues a proposed modification. Either parent has 30 days to request an administrative hearing before the change becomes final.
Through Circuit Court
The judicial path involves filing a Motion to Modify with the circuit court that issued your original order. This is the more common route when parents are already in other court proceedings or want a judge to weigh in on contested issues. Filing fees vary by county; in St. Louis County the fee is $137.50 as of 2025. After filing, you must formally serve the other parent through a process server or sheriff. Once served, the responding parent typically has 30 days to answer.
If both parents agree on the new amount, they can submit a joint agreement for the judge’s approval and skip a contested hearing. If there’s a dispute, the court schedules a hearing, both sides present evidence, and the judge enters a new order with the updated amount and effective date.
When the New Amount Actually Starts
This is the most misunderstood piece of the process. A modified Missouri child support order applies only to payments that come due after the other parent has been personally served with the motion.1Missouri Revisor of Statutes. Missouri Code 452.370 – Modification of Judgment as to Maintenance or Support It does not reach back and change what you owed for months before you filed. If your income dropped in January and you don’t file until June, those five months at the old rate are locked in.
Do not wait to file. Every month between the change in your circumstances and the date you serve the motion is a month you owe the full original amount, regardless of ability to pay. Courts have very limited authority to grant retroactive relief, generally only in cases involving fraud, misrepresentation of income, or clerical errors in the original order.
Equally important: keep paying the current amount until the court enters a new order. Cutting your payments on your own because you “know” a modification is coming does not protect you. Unpaid amounts accumulate as arrears and accrue interest, and no future modification wipes out what you already owed under the existing order.
What Happens if You Fall Behind Instead of Filing
Missouri’s enforcement tools are aggressive, and they’re the main reason to move quickly on a modification if you can’t afford your current amount.
Every dollar of past-due child support accrues simple interest at 1% per month, or 12% per year.5Missouri Revisor of Statutes. Missouri Code 454.520 – Delinquent Child Support and Maintenance, Interest On Interest is calculated at the end of each month on the total arrearage, and no payment is applied to interest until the underlying support balance is satisfied. The interest balance can grow for years untouched while you make partial payments.
FSD can order your employer to withhold child support directly from wages, salaries, commissions, bonuses, workers’ compensation, disability benefits, and retirement payments. Employers must transmit withheld amounts within seven business days and cannot fire you for being subject to a withholding order.6Missouri Revisor of Statutes. Missouri Code 454.505 – Income Withholding for Child Support The total withheld cannot exceed federal wage garnishment limits.
FSD can also order the Missouri Department of Revenue to suspend your driver’s license if you fall behind, under Sections 454.1000 through 454.1031 of Missouri’s revised statutes.7Missouri Department of Social Services. Driver License Suspension – Frequently Asked Questions Losing your license makes it harder to get to work, which makes it harder to earn what you need to catch up.
Persistent nonpayment can also become criminal. Criminal nonsupport in Missouri is a Class A misdemeanor. If your total arrearage exceeds 12 months’ worth of payments, the charge escalates to a Class E felony.8Missouri Revisor of Statutes. Missouri Code 568.040 – Criminal Nonsupport A conviction can result in probation conditioned on catching up, and if you violate that probation, the court can impose jail time. The arrearage does not go away after a conviction. You still owe every dollar plus interest.
If a modification is warranted, file it. Waiting only increases what you owe under an order that no longer fits your situation.