How Child Support Is Calculated in Montana

Courts must apply the Montana Child Support Guidelines adopted by the Department of Public Health and Human Services in every case, including defaults and agreements. The guideline amount is presumed adequate unless the court finds by clear and convincing evidence that it is unjust or inappropriate, and the court must state its reasons and the guideline amount. DPHHS describes the guidelines as a formula that considers the income of both parents, and it publishes the guideline worksheets, instructions, financial affidavit and tables (effective February 1, 2026). No online calculator was found on the DPHHS page.

You can enroll in child support services with the Department of Public Health and Human Services, Child Support Services Division (CSSD), using its online enrollment form, which CSSD says is the quickest and easiest way and is processed as soon as it is submitted. CSSD services include locating parents, establishing paternity, establishing financial and medical support orders, enforcing orders, and modifying orders.

Child support ends when the child is emancipated or graduates from high school (if enrolled), whichever is later, but no later than the child's 19th birthday, unless a written agreement or the decree expressly extends or waives the end date. Support for a child with a disability who is financially dependent on the custodial parent (who is the primary caregiver) does not end just because of age; it continues until the court finds the person is no longer disabled or no longer financially dependent, for orders issued or still in effect on or after July 1, 2019.

A support order can be modified only for payments due after the parties get actual notice of the motion, and only on a showing of changed circumstances so substantial and continuing that the terms are unconscionable, by written consent of the parties, or on application by the Department when it provides child support services (generally not within 12 months of the last order or modification). You can ask CSSD to review an order if at least 36 months have passed since it was entered or last reviewed; sooner, you must show a significant change, such as changed daycare or medical expenses or a change of at least 30% in a parent's income. You get a Request for Review packet from your CSSD investigator; CSSD recalculates support under the guidelines and serves a notice, and parents can correct information, consent, or request an administrative hearing. The process usually takes no more than 180 days.

Most support in Montana is collected through income withholding. Other CSSD enforcement tools include federal tax refund and federal administrative payment offset (IRS collection fees are passed on to non-public-assistance recipients), state payment offset through the Department of Revenue, credit bureau reporting, passport denial, suspension of driver's, occupational and recreational (hunting and fishing) licenses, interception of Montana Lottery winnings of $600 or more, freezing and seizing bank accounts, garnishments, inheritances and insurance settlements, and liens on real and titled personal property in Montana.

Montana's child support agency is the Child Support Services Division (CSSD) of the Department of Public Health and Human Services. CSSD locates parents, establishes paternity, establishes, enforces and modifies support orders (including medical support), handles intergovernmental cases and runs the central case and support order registry. Enroll for services online (the quickest way to start) or contact a local child support office. Payments can be made through the Online Payment Portal from a bank account or by credit/debit card, and payment history can be checked through the Montana Child Support Payment Lookup or the phone system. Phone: 1-800-346-5437.

Montana does not publish an online child support calculator on its official guidelines page. The Child Support Services Division (CSSD) of the Department of Public Health and Human Services publishes the Montana Child Support Guidelines, Guidelines Worksheets and Instructions, and the Guidelines Tables (effective February 1, 2026). The guidelines use a formula that considers the income of both parents, and state law requires the district court, CSSD and the Office of Administrative Hearings to use them in all child support cases.