A Montana child support order can be changed, but only going forward and only through the court or the Child Support Services Division. A district court may modify support on a showing of changed circumstances "so substantial and continuing as to make the terms unconscionable," on the parties' written consent, or on the Department's application (MCA § 40-4-208(2)(b)). The Division can also review and modify an order through its own administrative process (MCA §§ 40-5-272, 40-5-273). This page is part of our Montana Divorce Guide.
The Grounds for a Court Modification
| Ground | What the statute requires | MCA |
|---|---|---|
| Changed circumstances | A showing of changed circumstances "so substantial and continuing as to make the terms unconscionable." | § 40-4-208(2)(b)(i) |
| Written consent | Both parties consent in writing. The court still applies the guidelines to the new amount. | §§ 40-4-208(2)(b)(ii), 40-4-204(3) |
| Department application | The Department of Public Health and Human Services applies, when it is providing child support services in the case. | § 40-4-208(2)(b)(iii) |
| Medical support | There is no medical support order, or one has been violated. This justifies an immediate modification. | § 40-4-208(2)(c) |
Whatever the ground, "the support obligation must be modified, as appropriate, in accordance with the guidelines" (MCA § 40-4-208(2)(b)). A modification is a fresh guidelines calculation with current numbers. The same subsection states that a modification under it may not be made within 12 months after the order was established or most recently modified.
The phrase "substantial and continuing" does two jobs. The change has to be large, and it has to be lasting. The statute does not put a figure on either word, and courts decide the question on the facts of each case.
No Retroactive Changes Before Notice
The most important limit is timing. A decree "may be modified by a court as to maintenance or support only as to installments accruing subsequent to actual notice to the parties of the motion for modification" (MCA § 40-4-208(1)).
In practice this means the clock starts when the other parent has actual notice of your motion, not when your income dropped or the schedule changed. Support that came due before then is owed at the old amount. If your circumstances have changed in a lasting way, acting promptly matters more here than almost anywhere else in family law. See unpaid child support and interest.
Administrative Review Through the Division
The district court is not the only route. On the application of the Department, the obligor, or the obligee, the Child Support Services Division may review a district court or administrative support order "to determine whether the support order should be modified in accordance with the guidelines" (MCA § 40-5-272(1)). The Division's rule limits this review to orders it is enforcing in an open case (ARM 37.62.2101(1), 37.62.2103(2)(b)). The statute lists sufficient grounds for review (MCA § 40-5-272(4)):
- a substantial change in circumstances as defined by administrative rule;
- the need to provide for the child's health care needs;
- a lapse of 36 months from the date the order was entered, a review hearing was granted, or a modification was denied; or
- a change in custody of the child.
The rule defines a substantial change to include an increase or decrease of at least 30% in a parent's income for child support, the adoption, emancipation, or death of a child when the order is not a per child amount, a child's permanent move from one parent's home to the other's, and a child's development of special needs not considered in the original order (ARM 37.62.2103(1)).
The parties receive a notice of administrative review and, where appropriate, an order to produce financial information within 20 days of service. Any party may request a hearing (MCA § 40-5-273). The Department must make available forms and procedures that allow a parent to complete the review process without a lawyer (MCA § 40-5-272(6)).
Limited Review and Negligible Changes
A narrower process, the limited review, addresses a single change that is not caused by a change in either parent's income. It is available for a change in parenting time or a child's residence, a change in day care needs expected to last at least 18 months, new or ended special needs, a change in the child's health insurance cost equal to 25% of the support order and expected to last at least 18 months, the birth of another child to the parties, and a child reaching majority, becoming emancipated, marrying, entering military service, or dying (MCA § 40-5-278).
Not every recalculation leads to a new amount. If the difference between the existing order and the proposed obligation is less than 15%, the Division may treat the change as negligible and leave the support amount alone, although it may still add or update medical support provisions (MCA § 40-5-277(4); ARM 37.62.2117).
Job Loss, Incarceration, and Other Common Changes
A drop in income does not automatically lower support. The guidelines allow income to be imputed to a parent who is unemployed or underemployed, based on work history, qualifications, and local job opportunities (ARM 37.62.106). See what counts as income for child support.
Incarceration is treated differently. Income is not imputed to a parent incarcerated for more than 180 days (ARM 37.62.106(6)(b)), and the Division may review an order it is enforcing when it receives documentation that the obligated parent will be incarcerated for more than 180 days. The result may be abatement of support during the incarceration and for 60 days after release (ARM 37.62.2101(3)).
A change in the parenting schedule is addressed in parenting time and child support, and changing the plan itself in amending a parenting plan.
Agreeing on a New Amount
Parents who agree can use the written consent route, which avoids having to prove unconscionability. The agreement still has to be submitted, the guidelines still apply, and a variance from the guidelines amount still needs stated reasons (MCA § 40-4-204(3)). Until a new order is entered, the old one controls. Our page on agreements about child support explains why. For other parts of a decree, see can you change a divorce decree later.
This page explains Montana law in general as of the 2025 Montana Code Annotated and the current administrative rules. It is not legal advice about your specific case.