Child Support Calculations in Montana

Montana uses a unique Melson-style formula under ARM 37.62—not the Income Shares or Percentage-of-Income models used by most states. Whether you're navigating an uncontested or contested divorce, understanding the personal allowance, primary child allowance, and Standard of Living Adjustment (SOLA) is essential.

The Melson-Style Formula

Montana's three-step approach protects each parent's basic self-support first, funds the child's primary needs, then adds a percentage of remaining income (SOLA) so children share in their parents' standard of living.

• Personal Allowance (Self-Support Reserve): $20,345/year (2025)—130% of federal poverty guideline
• Primary Child Support Allowance: $6,104/year for 1 child (based on poverty guidelines)
• SOLA: 14% for 1 child, 21% for 2, 27% for 3, up to 47% for 8+ children
• No combined income cap: Unlike Income Shares states, Montana has no table ceiling

What Counts as Income

Under ARM 37.62.105, gross income includes:

• Employment income: Wages, tips, commissions, bonuses, mandatory overtime
• Self-employment: Net business income (with straight-line depreciation adjustments)
• Benefits: Social Security, pensions, veterans benefits, workers' comp, unemployment, disability
• Investment income: Interest, dividends, trust income, annuities
• Other: EITC, severance, spousal support received

Exclusions

• New spouse's income
• Means-tested benefits: TANF, SSI, SNAP
• Child support received for other children
• Adoption subsidies (unless that child is in the calculation)

Step-by-Step Calculation

1. Calculate income after deductions: Start with gross income, subtract allowable deductions (taxes, FICA, ordered support for others, mandatory retirement, required work expenses)
2. Subtract personal allowance: $20,345 from each parent to get "income available for child support"
3. Calculate percentage shares: Use the higher of "income available" or 12% of income after deductions
4. Determine primary allowance: From 2025 tables ($6,104 for 1 child, $10,173 for 2, etc.)
5. Add supplements: Net child care, child-only health insurance, recurring medical >$250/year
6. Apply SOLA: Multiply remaining income by SOLA percentage (14-47%)
7. Credit for direct payments: Reduce for add-ons actually paid by each parent

2025 Allowance Amounts

From the 2025 Guidelines Tables (CS 404.2):

• Personal allowance: $20,345/year per parent
• Primary child support allowance: 1 child = $6,104; 2 = $10,173; 3 = $14,242; 4 = $16,276
• IRS mileage (long-distance): $0.70/mile
• Standard travel expense: $1,400 (2,000 miles baseline)

Need a Detailed Support Estimate?

Montana uses official worksheets (Worksheets A-E) for child support calculations. Download them from CSSD's worksheet page. For a guided walkthrough covering personal allowances, SOLA percentages, parenting-time adjustments, and add-on expenses, try our planning tool.

Shared Parenting (110-Day Threshold)

Montana's shared parenting adjustment triggers when at least one child spends more than 110 days per year with each parent:

• ≤110 days with non-residential parent: Standard calculation—non-residential parent pays their full annual obligation
• >110 days with both parents: Use Worksheet B—allocate each parent's obligation by days with each parent, then offset
• Split custody: Same Worksheet B method—compute per-child obligations and offset
• "Day" definition: Majority of a 24-hour period; school/daycare days belong to "primary contact" parent

Long-Distance Parenting Adjustment

If annual travel to exercise parenting time exceeds 2,000 miles:

• Adjustment formula: (Total miles × $0.70) − $1,400 standard expense
• Application: Reduces SOLA-available income (not the basic obligation)
• Transportation only: Meals and lodging not included
• Cannot reduce SOLA below zero

Add-Ons to Basic Support

• Child care: Net cost after federal dependent care credit (work/education-related)
• Health insurance: Child-only premium or incremental cost to add children
• Extraordinary medical: Recurring predictable uninsured costs >$250/child/year
• Other recurring needs: May be added with credit to paying parent

Duration of Support

Under MCA 40-4-208:

• Standard termination: Emancipation or high school graduation (whichever later)
• Maximum age: 19th birthday (absolute cap unless extended)
• Disabled adult dependents: Support continues if child has disability (onset before 18), is financially dependent, and custodial parent is primary caregiver

Modification Standards

Through CSSD administrative review or court:

• 36-month review: Available without showing any change
• Early review (within 36 months): Requires significant change (30% income change, custody change, changed expenses)
• Court modification: "Substantial and continuing change" standard; generally not within 12 months

Enforcement Tools

Montana CSSD can enforce through:

• Immediate income withholding
• Tax refund intercepts: Federal and state
• License suspension: Driver's, professional, recreational (60-day cure window)
• Passport denial/hold
• Bank levies and property liens
• Lottery intercepts: Winnings ≥$600
• Credit bureau reporting

Interest on Arrears

Under MCA 25-9-205:

• Interest rate: Bank prime rate + 3% (set annually on January 1)
• Compounding: None (simple interest)
• Automatic accrual: Montana Supreme Court has held interest accrues automatically even if decree is silent

Common Calculation Mistakes

• Expecting an Income Shares table: Montana uses Melson-style, not combined-income lookup tables
• Forgetting the personal allowance: $20,345 must be subtracted before calculating income available
• Not using net child care: Must subtract federal dependent care credit
• Misunderstanding the 12% floor: Support can't be less than 12% of income after deductions (if above personal allowance)
• Ignoring SOLA: Critical step that increases support when parents have remaining income
• Using overnight counts alone: "Day" is majority of 24-hour period, not just overnight

Key Takeaways

• Melson-style formula: Personal allowance → primary child allowance → SOLA
• $20,345 personal allowance: Self-support reserve (130% poverty guideline)
• $6,104 primary allowance: Per first child (2025)
• SOLA: 14-47% of remaining income based on number of children
• 110-day shared threshold: Triggers Worksheet B allocation
• No combined income cap: Unlike Income Shares states
• 36-month review: No change showing required
• Prime + 3% arrears interest: Simple, not compound
• Age 19 maximum: Unless disabled adult dependent

For more information about Montana divorce processes, see our Montana divorce timeline and filing checklist. For property division information, review our Montana marital property guide.