Quick answer: Montana uses the modified Melson formula of the Child Support Guidelines (ARM 37.62.101 to 37.62.148), applied through the Child Support Services Division worksheets. Each parent’s income after taxes, Social Security, mandatory retirement, work expenses, other children and maintenance is reduced by a personal allowance ($20,748 a year per parent, with the tables effective February 1, 2026). The income left is each parent’s income available for child support; the parents’ shares of the combined amount are applied to the children’s primary allowance ($6,224 for one child, $10,374 for two, up to $24,897 for eight) plus child care, health insurance and other supplements. Each parent also owes a standard of living adjustment (SOLA) of 14% to 47% of the income left after his or her share. A parent receives credit for the expenses he or she pays, and the days each parent has the children set the payment: with 110 days or fewer, the fewer-days parent pays his or her annual obligation in 12 payments; with more than 110 days, a per-child credit applies and the two obligations are offset. The result is a rebuttable presumption.
How the Montana worksheets work
- Income after deductions. Lines 1 to 3.
- Personal allowance and shares. Lines 4 to 9. See how the Melson formula works.
- Primary allowance and supplements. Lines 10 to 13. See minimum support and supplements.
- SOLA, credits and parenting days. Lines 14 to 27. See parenting days and the 110-day rule.
What this calculator checks
The calculator follows Worksheets A to E and the 2026 tables, and was checked against an independent per-child re-implementation. It assumes the same number of days for every child and does not apply the long-distance parenting adjustment, standard-of-living variances or deviations; enter child care after the dependent care credit.
Child support across Montana
The guidelines apply in every Montana district court, from Billings, Missoula, Great Falls, Bozeman, Butte or Helena, and in the Child Support Services Division’s administrative cases. The result is a presumption; the court must explain any variance in terms of the child’s best interests.
Frequently asked questions
How is child support calculated in Montana?
With the modified Melson formula: each parent keeps a personal allowance, the income left is shared, the children's primary allowance and supplements are divided by those shares, and a standard of living adjustment applies to higher incomes.
What is the Montana personal allowance?
$20,748 a year for each parent in the tables effective February 1, 2026.
What is the Montana primary child support allowance?
$6,224 a year for one child, $10,374 for two, $14,523 for three, and so on up to $24,897 for eight.
What is the Montana 110-day rule?
If the children spend 110 days or fewer a year with one parent, that parent pays his or her annual obligation in monthly payments; above 110 days, a per-child credit and an offset apply.
What is the Montana standard of living adjustment?
A percentage of the income left after a parent's share of the primary allowance: 14% for one child up to 47% for eight.