Montana Child Support and Custody: The 110-Day Rule and Melson Formula Explained

Montana is one of only three states that uses a Melson-style child support formula — a three-tier calculation that first protects each parent's basic living needs before allocating support for the child. Your parenting time schedule directly determines how much child support is owed, because Montana uses the 110-day threshold to switch between two different calculation worksheets.

Understanding this connection is essential before you finalize your parenting plan.

The 110-Day Threshold

Montana child support guidelines define a "day" as the majority of a 24-hour period (more than 12 hours). The overnight count determines which worksheet the court uses:

Worksheet A (Standard): Applies when the non-residential parent has 110 overnights or fewer per year. The non-residential parent pays the full calculated support amount. No parenting-time adjustment is applied.

Worksheet B (Shared Parenting): Applies when both parents have more than 110 overnights per year. Each parent's obligation is calculated separately, then offset against the other's. The parent with the higher remaining obligation pays the net difference.

In practice, Worksheet B typically results in a significantly lower net child support payment compared to Worksheet A for the same income levels, because it accounts for the direct costs both parents incur when the child is in their care.

How the Melson Formula Works

Montana's Melson formula operates in three tiers:

Tier 1: Self-Support Reserve

Before calculating any child support, the formula deducts a personal allowance from each parent's gross income — ensuring neither parent falls below a basic standard of living. For 2026, the personal self-support allowance is $20,748 per year per parent.

If a parent's income falls below this threshold, their support obligation is limited to a nominal minimum (typically $50 per month).

Tier 2: Primary Child Support Allowance

After the self-support reserve is subtracted, the formula calculates the child's basic financial needs. For 2026, the primary child support allowance is $6,224 per year for the first child. Additional children increase the allowance.

Added to this primary allowance are documented supplemental expenses:

• Net cost of employment-related childcare
• Child-only health, dental, and vision insurance premiums
• Unreimbursed extraordinary medical or educational expenses exceeding $250 per year

Tier 3: Standard of Living Adjustment (SOLA)

If a parent has income remaining after covering both the self-support reserve and their share of the primary child support allowance, the SOLA percentage is applied to that remaining income. This ensures children share in their parents' standard of living when parents earn well above the poverty line.

SOLA rates:

• 1 child: 14% of available remaining income
• 2 children: 21%
• 3 children: 27%
• Scaling up to 47% for 8+ children

Montana does not cap combined parental income for the SOLA calculation.

What Counts as Gross Income

The court includes all sources: wages, salaries, commissions, overtime, bonuses, self-employment earnings, investment income, rental income, and unemployment benefits. If a parent is voluntarily unemployed or underemployed to reduce their support obligation, the court may impute income based on their earning capacity, work history, and education.

How Parenting Time Affects the Calculation

The financial impact of even a few overnights can be substantial near the 110-day threshold. A schedule that gives the non-residential parent exactly 110 overnights uses Worksheet A. Adding one more overnight — 111 — switches to Worksheet B, potentially reducing the net monthly payment by hundreds of dollars depending on both parents' incomes.

This is why Montana custody disputes sometimes become battles over individual overnights. Both parents need to understand the financial implications of their proposed schedule before they commit to it.

Extraordinary Expenses

Costs like extracurricular activities, school field trips, tutoring, and music lessons are not automatically included in the child support calculation. Your parenting plan must explicitly state how these expenses are shared — commonly split 50/50 or in proportion to each parent's gross income — and describe the reimbursement process (receipts, timelines, dispute resolution).

Tax Considerations

The primary residential parent generally claims the child as a dependent for federal and state tax purposes. However, the court can allocate the dependent exemption to the non-residential parent (via IRS Form 8332) if doing so maximizes the family's net disposable income — typically when the non-residential parent is in a higher tax bracket and current on all support obligations.

Calculate Before You Negotiate

Too many parents negotiate their parenting schedule without understanding the child support consequences. The Montana Child Custody & Parenting Plan Guide includes an overnight-counting worksheet and walks you through both Worksheet A and Worksheet B calculations — so you know exactly how your proposed schedule translates to dollars before you sign anything.

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