How to Modify Child Support in Montana: Filing Steps and Effective Date

By the FigureMyTax Editorial Team · How we calculate

To modify Montana child support, file a motion or apply to the department for a review, and make sure the other parent has actual notice. Only installments accruing after actual notice can change.

How do you modify child support in Montana?

1. Run the guideline amount in the Montana child support calculator and see the gap in the modification calculator.
2. File a motion to modify with the court (MCA 40-4-208), or apply to the department for a review (40-5-272).
3. Make sure the other parent has actual notice: only installments accruing after actual notice of the motion can change (40-4-208(1)).
4. Show the change and check the 12-month wait.
5. Keep paying the existing order until it is changed.

Why does actual notice matter in Montana?

Because the statute lets a decree be modified only as to installments accruing after actual notice to the parties of the motion for modification (40-4-208(1)). A motion that is filed but not noticed does not start the clock. Serve promptly and keep proof.

How does a Montana department review work?

The department may review the order on application by itself, the obligor or the obligee, and a review can be requested without a lawyer, using forms the department must make available. Grounds include a rule-defined substantial change, health care needs, a lapse of 36 months and a change in custody. A party may withdraw a request before the department issues its notice, and then the other party can continue by written request (40-5-272(4)-(6)).

What is a Montana limited review?

A narrower review for a specific change that is not a change in net income. It is available for a change in parenting time or residence with no modified order yet, a day-care need that has changed and will last at least 18 months, new special needs lasting at least 18 months, a change of 25% of the order in the cost of the child’s health insurance expected to last 18 months, the birth of another child to the parties, or a child who has reached majority or is emancipated, married or in the armed forces (40-5-278). The recommendation is limited to adding or subtracting the value of the change.

What if the order does not mention medical support?

Every support order and modification must include a medical support order (40-4-204(4)); if it is missing, you can seek an immediate modification to add it (40-4-208(2)(c)).

What guidelines does the court apply on a modification?

The court must apply the uniform child support guidelines in every case, including defaults and agreements; the guideline amount is presumed adequate and reasonable unless the court finds by clear and convincing evidence that it is unjust or inappropriate, and it must state its reasons (40-4-204(3)).

Does a temporary job change count as continuing?

A temporary layoff that ends within weeks is hard to call continuing, so wait to see whether the change will last and keep records of how long it has. If it lasts, give notice then.

Can both parents ask for a review at once?

Yes. A party may withdraw a department review request before the notice is issued, and after the notice the other party can continue by filing a written request to continue (40-5-272(5)). That means a review you start can be finished by the other side.

How much does a late motion cost? An example

If notice happens 3, 6 or 9 months after your change, the relief you lose at a $300 monthly difference is:

What happens to unpaid support while the motion is pending?

It stays owed. See how long Montana arrears last and add up your balance.

Frequently asked questions

Official sources

• MCA 40-4-208: modification and termination of support
• MCA 40-4-204: child support orders; guidelines; withholding
• MCA 40-5-272: application for review of child support orders
• MCA 40-5-278: limited review of support order
• 42 U.S.C. 666(a)(9): no retroactive modification of support already due

This is general information, not legal advice. It is based on the cited Montana statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Montana attorney.