How Montana Calculates Child Support: The Melson Formula
Montana lets each parent keep a personal allowance of $20,748 a year, shares the income left in proportion to income available to cover the children’s primary allowance and supplements, adds a standard of living adjustment of 14% to 47%, and credits the expenses each parent pays.
Step 1: Income after deductions
Add each parent’s income (wages, self-employment, pensions, unearned and imputed income, EITC, other taxable and non-taxable income) and subtract federal and state income tax, Social Security and Medicare, mandatory retirement contributions, required employment expenses, ordered support and an allowance for other children, ordered alimony and similar items (Worksheet A, lines 1 to 3). All amounts are annual and rounded to whole dollars.
Step 2: Personal allowance and shares
Each parent keeps a personal allowance, $20,748 a year in the tables effective February 1, 2026 (Table 1). Income available for child support is income after deductions minus the allowance, never below zero (line 5). Line 6 is 12% of income after deductions (or the minimum contribution if income is below the allowance); line 7 is the higher of lines 5 and 6, and each parent’s share is line 7 divided by the combined line 7.
Step 3: Primary allowance and supplements
The children’s primary allowance comes from Table 2 by the number of children: $6,224, $10,374, $14,523, $16,598, $18,673, $20,748, $22,822 or $24,897 for one to eight. Child care (after the dependent care credit), the children’s health insurance premium, unreimbursed medical costs over $250 per child and other costs are added (line 13). See minimum support and supplements.
Step 4: Standard of living adjustment
Each parent’s share of line 13 is capped at his or her income available (line 16); what remains (line 17) is multiplied by the SOLA factor: 14% for one child, 21% for two, 27% for three, 31% for four, 35% for five, 39% for six, 43% for seven and 47% for eight. The obligation is line 16 plus the SOLA, with a floor at line 6, less credit for the supplemental expenses the parent pays (lines 21 to 24).
A worked example
Two children live mainly with the parent who earns $36,000 a year; the other parent earns $72,000 and has no overnights.
| Line | Amounts |
|---|---|
| Annual income after deductions: majority-days parent / fewer-days parent (line 3) | $30,746 / $57,992 |
| Less personal allowance, $20,748 each; income available (line 5) | $9,998 / $37,244 |
| Minimum 12% of income (line 6) | $3,690 / $6,959 |
| Share of combined income available (line 9) | 21.2% / 78.8% |
| Primary allowance for two children (line 11) | $10,374 |
| Each parent’s share of the allowance (line 15) | $2,195 / $8,179 |
| Income left for SOLA (line 17) | $7,803 / $29,065 |
| SOLA at 21% (line 20) | $1,639 / $6,104 |
| Annual obligation (line 24) | $3,834 / $14,283 |
| Monthly transfer: fewer-days parent pays | $1,190 |
The Montana child support calculator reproduces this example; with 100 days the same $1,190 applies (110 days or fewer), and with 130 days it falls to $982. See parenting days.
What to gather
Tax returns and pay records for both parents, orders for other children, maintenance orders, child care and insurance statements and a calendar of the actual days.
Rounding
Cents are rounded to whole dollars at each line: $0.49 or less down, $0.50 or more up.
Frequently asked questions
What is the Melson formula in Montana?
A formula that protects each parent's personal allowance, shares the income left to cover the children's primary allowance and adds a standard of living adjustment.
What income does Montana use for child support?
Income after deductions for taxes, Social Security, mandatory retirement, work expenses, other children and ordered alimony.
Does Montana child support rise with income?
Yes. The standard of living adjustment applies to income above a parent's share of the primary allowance.
How many children does the Montana table cover?
One to eight, with larger primary allowances for each additional child.
Is the Montana guideline amount presumptive?
Yes. It is a rebuttable presumption, and variances need findings in the child's best interests.
Official sources
- Montana Child Support Guidelines Worksheets A to E and Instructions
- Montana Child Support Guidelines: ARM 37.62.101 to 37.62.148
- CSSD Policy 404.2 Guidelines Tables, effective February 1, 2026
A local family law attorney can review your situation — many offer a free consultation.
This is general information, not legal advice. It is based on the cited Montana statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Montana attorney.