Quick answer: In Missouri, child support can be modified only on changed circumstances so substantial and continuing as to make the terms unreasonable. A guideline change of 20% or more is a prima facie showing if the existing amount was based on the presumed guideline amount. Only installments that accrue after service of the motion can be changed. Support is stated in monthly amounts.
This Missouri child support modification calculator applies RSMo 452.370. Enter your current order and the amount the guidelines give today (you can get it from the Missouri child support calculator), say whether the existing order followed the presumed amount, and it shows whether the 20% prima facie showing is met, the monthly gap and what it adds up to after service.
Missouri child support modification at a glance
| Rule | What Missouri says |
|---|---|
| Standard | Changed circumstances so substantial and continuing as to make the terms unreasonable (RSMo 452.370.1) |
| 20% showing | A guideline change of 20% or more is a prima facie showing, if the existing amount was based on the presumed guideline amount (452.370.1) |
| What the court considers | All financial resources of both parties, including expenses shared with a cohabitant, and the earning capacity of a party who is not employed (452.370.1) |
| Start date | Only installments that accrued after the date of personal service (452.370.6) |
| IV-D cases | In a case filed by the Family Support Division the court shall modify if the current amount differs from the guideline amount (452.370.8); a review comes first (454.496) |
| Emancipation notice | The parent receiving support must tell the paying parent of emancipation or owe back what was paid after it, plus interest (452.370.4) |
How does child support modification work in Missouri?
- Know the standard and the 20% showing. See what counts as a substantial and continuing change in Missouri.
- File and serve on time. See how to modify child support in Missouri.
- Income problems and incarceration. See lowering child support after job loss or incarceration in Missouri and, for what stays owed from before service, the Missouri child support arrears calculator.
What does this modification calculator check?
The calculator tests the 20% line against the weekly-to-monthly guideline amount you enter and tells you whether the shortcut applies, which depends on whether the existing order followed the presumed amount. It shows the monthly gap and the accrued difference after service. It cannot decide whether a court will find the change substantial and continuing.
Frequently asked questions
How much does child support have to change to be modified in Missouri?
A guideline change of 20% or more is a prima facie showing of a substantial and continuing change, if the existing amount was based on the presumed guideline amount. A smaller change can still be proven.
From what date can Missouri child support change?
Only for installments that accrued after the date of service of the motion.
Does a Missouri deviation order get the 20% shortcut?
No. The prima facie showing applies only if the existing amount was based on the presumed guideline amount.
Does a new spouse's income count in a Missouri modification?
The court considers all financial resources of both parties, including the extent to which expenses are shared with a spouse or other person they live with.
Does Missouri require the receiving parent to report emancipation?
Yes. A parent who fails to notify the paying parent is liable for support paid after emancipation, plus interest.