Montana child support calculator

How Montana calculates child support

• Montana uses a Melson formula on annual amounts. Each parent’s income is reduced by allowable deductions, including the income tax and Social Security they actually pay, other children they support and ordered alimony, and then by a $20,748 personal allowance.
• Every parent owes at least a minimum contribution: 12% of income after deductions, or a smaller percentage from the Worksheet C table when income after deductions is below the personal allowance.
• The children’s primary allowance is $6,224 a year for one child ($10,374 for two, $14,523 for three), plus child care, the children’s health insurance and recurring medical costs over $250 a child. Each parent owes a share by income, then a Standard of Living Adjustment of 14% of remaining income for one child up to 47% for eight or more.
• When the children live mainly with one parent and spend no more than 110 days a year with the other, the other parent pays their annual amount in monthly installments. When a child spends more than 110 days with each parent, or the children are split between homes, each child’s support is allocated by days (a 0.0069 credit for each day over 110) and offset.

What the calculator asks

• How many children is the support for?
• Where do the children live most of the time?
• How many days a year do the children spend with the parent they do not mainly live with?
• How many of the children live mainly with you?
• Your total income for the year
• Federal income tax you owe for the year
• Montana (state) income tax you owe for the year
• Social Security and Medicare taxes you pay for the year
• Mandatory retirement contributions for the year
• Child support you pay under an order for other children (per year)
• How many of your other children live with you without a support order?
• Alimony or spousal support you are ordered to pay (per year)
• Required work expenses you pay (per year)
• Other allowable deductions (per year)
• The other parent’s total income for the year
• Federal income tax the other parent owes for the year
• State income tax the other parent owes for the year
• Social Security and Medicare taxes the other parent pays for the year
• The other parent’s mandatory retirement contributions for the year
• Child support the other parent pays under an order for other children (per year)
• How many of the other parent’s other children live with them without a support order?
• Alimony or spousal support the other parent is ordered to pay (per year)
• Required work expenses the other parent pays (per year)
• The other parent’s other allowable deductions (per year)
• Child care you pay for these children so you can work (per year), minus the dependent care tax credit
• Child care the other parent pays for these children (per year), minus the dependent care tax credit
• What you pay to cover these children on health insurance (per year)
• What the other parent pays to cover these children on health insurance (per year)
• Recurring uninsured medical costs you pay for these children above $250 a child (per year)
• Recurring uninsured medical costs the other parent pays above $250 a child (per year)
• Does either parent travel more than 2,000 miles a year for parenting time?
• Do the children receive Social Security or veterans benefits because of a parent’s earnings or service?

It never asks for names, Social Security numbers or account numbers, and your answers are not saved.

What the estimate leaves out

• Long-distance parenting travel adjustments (Worksheet D)
• Social Security or veterans benefits the children receive because of a parent’s earnings or service (ARM 37.62.144)
• Imputed income: the court or CSSD may count full-time earnings a parent could make (ARM 37.62.106)
• Other special needs of the children (worksheet line 12d) and other SOLA adjustments (line 18b)
• Children cared for by a third party instead of a parent
• Variances from the guidelines amount, which need written findings (ARM 37.62.102)

When a situation is outside what the calculator covers, it says so and points you to the official worksheet instead of guessing.

Official sources

• CSSD Policy 404.2, Montana Child Support Guidelines Tables (effective February 1, 2026)
• Montana Child Support Guidelines, ARM 37.62.101–148 (DPHHS copy, 2023-04-06)
• Montana Child Support Guidelines Worksheets (A–E) & Instructions (rev. 2025-08-12)
• CSSD Policy 404.1, Child Support Guidelines

Montana Child Support Guidelines worksheets and tables (DPHHS Child Support Services Division) →