Montana Child Support Calculator

Montana uses the Income Shares model. Income-shares model based on combined gross income and number of children per Montana ARM 37.62; each parent's obligation prorated by income share; adjusted for parenting days and add-ons (childcare, health insurance).

Montana's guideline runs on gross. That distinction matters: entering gross income into a formula built on net income (or the reverse) produces a materially wrong figure. Most states count income from essentially any regular source -- wages, self-employment, bonuses, commissions, rental and investment income, and many benefits -- not just salary.

Not necessarily. Montana's guideline weighs each parent's share of combined income alongside the parenting-time arrangement, so a significantly higher earner can still owe support even at an even split of time.

Yes. The figure produced by Montana's Income Shares guideline is presumptive, not mandatory: a court can order a different amount when applying the guideline would be unjust or inappropriate for the specific case, and generally must state its reason on the record. Common grounds include extraordinary medical or educational expenses, a child's special needs, or costs the formula does not capture.

You have to file for a modification -- a change in your circumstances does not change what you owe on its own. Montana, like most states, requires a substantial change in circumstances: a significant involuntary income change, a change in the parenting schedule, or a material change in the child's needs. Until a court or the state child support agency issues a new order, the existing amount stays fully enforceable and arrears keep accruing, and a modification is generally not applied retroactively before the date you filed -- so filing promptly matters. In Montana, modifications are handled through Child Support Services Division — Montana DPHHS.

Montana publishes it directly: "Child Support Forms — Montana Courts". This site's calculator is a fast estimate built on the same published guideline, not a replacement for the official form -- a court filing generally requires the state's own worksheet. The link is in the Montana Resources section on this page.