What Counts as a Substantial and Continuing Change for Child Support in Missouri
In Missouri, a guideline change of 20% or more is a prima facie showing of a substantial and continuing change if the existing order followed the presumed amount. A change can start only from the date of personal service.
What is a substantial and continuing change for child support in Missouri?
The standard is changed circumstances so substantial and continuing as to make the terms unreasonable (RSMo 452.370.1). In deciding whether it has happened the court considers all financial resources of both parties, including the extent to which the reasonable expenses of either are or should be shared by a spouse or other person they live with, and the earning capacity of a party who is not employed.
What is the 20% showing?
If applying the guidelines and the supreme court rules to the parties’ finances would change child support from the existing amount by 20% or more, a prima facie showing has been made of a change so substantial and continuing as to make the terms unreasonable, if the existing amount was based on the presumed guideline amount (452.370.1). The Missouri child support modification calculator tests it.
| Existing monthly order | Guideline at or above | or at or below |
|---|---|---|
| $200 | $240 | $160 |
| $500 | $600 | $400 |
| $800 | $960 | $640 |
| $1,500 | $1,800 | $1,200 |
With an $800 order, $1,000 is 25% higher and meets the line; $900 does not.
Why does a deviation matter in Missouri?
The 20% shortcut applies only if the existing amount was based on the presumed guideline amount. If the court or the parents departed from the guidelines when the order was made, you cannot rely on the shortcut and must prove the change another way.
Is a smaller change enough in Missouri?
It can be, but you carry the burden. The court looks for a lasting change, not a temporary one, such as a long-term change in income, in the child’s needs or in parenting time. Appeals decisions the statute cites held that small or short-lived changes were not enough.
Does the court look at the child’s needs too?
Yes. Support is figured under the guidelines and criteria of section 452.340 once the party seeking modification has met the burden (452.370.2), which looks at the child’s needs and resources and both parents’ resources and standard of living.
Does it work differently when the state is involved?
Yes. In a IV-D case filed by the Family Support Division, the court shall modify the order under the guidelines if the current amount differs from the amount the guidelines would order, notwithstanding the requirement of a substantial and continuing change (452.370.8). The division first reviews the case (454.496.1).
From what date can the order change?
The order may be modified only as to support installments that accrued after the date of personal service (452.370.6; 454.496.4). Every month before service is lost:
| Monthly difference | Lost after 6 months | Lost after 12 months |
|---|---|---|
| $100 a month | $600 | $1,200 |
| $200 a month | $1,200 | $2,400 |
| $400 a month | $2,400 | $4,800 |
Federal law also bars retroactive modification of support already due (42 U.S.C. 666(a)(9)).
What happens next?
Read how to modify child support in Missouri for the filing steps, and check what stays owed with the Missouri arrears calculator.
Frequently asked questions
What is the Missouri 20% rule for child support modification?
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.
Does the Missouri 20% rule apply to a deviation order?
No. It applies only if the existing amount was based on the presumed guideline amount.
What does the Missouri court consider in a modification?
All financial resources of both parties, shared expenses with a cohabitant and the earning capacity of a party who is not employed.
Can Missouri change support that came due before service?
No. Only installments that accrued after the date of personal service.
Does Missouri modify a IV-D order without a substantial change?
Yes. In a case filed by the Family Support Division the court shall modify if the amount differs from the guidelines.
Official sources
- RSMo 452.370: modification of support
- RSMo 452.340: child support; termination
- RSMo 454.496: motion to modify in IV-D cases
- 42 U.S.C. 666(a)(9): no retroactive modification of support already due
A local family law attorney can review your situation — many offer a free consultation.
This is general information, not legal advice. It is based on the cited Missouri statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Missouri attorney.