The Foundation: Montana’s Income Shares Model

Quick Answer: Child support in Montana is calculated using the Income Shares Model under Administrative Rules of Montana (ARM) Title 37, Chapter 62. Both parents’ incomes are combined, a personal allowance is subtracted from each, and a base support amount is determined. That base is then adjusted for childcare costs, health insurance, parenting time, and a Standard of Living Adjustment (SOLA). The parent with less parenting time typically makes a transfer payment to the other parent. Courts must use the official guidelines worksheet in every case.

If you are going through a divorce, separation, or parenting plan case in Missoula, MT, one of your first questions is almost certainly: how is child support calculated in Montana? The answer is more specific — and more formula-driven — than most people expect.

Montana uses a detailed, multi-step calculation governed by state administrative rules. It is not a simple percentage of one parent’s income. It accounts for both parents’ earnings, parenting time, childcare costs, health insurance, and more. Understanding how it works helps you enter the process informed — and helps you identify situations where the standard result might not be fair for your family.

This article walks through the full Montana child support formula in plain English, based directly on the official Administrative Rules of Montana (ARM) Title 37, Chapter 62. Because the calculation involves many individual variables, the numbers in your case may differ significantly from any example shown here. Always verify the specifics of your situation with a licensed Montana family law attorney before making any financial decisions.

The Foundation: Montana’s Income Shares Model

Montana uses what is called the Income Shares Model to calculate child support. This is the most common approach in the United States, used in more than 40 states.

The core idea behind the Income Shares Model is straightforward: children should receive the same proportion of their parents’ combined income that they would have received if both parents were still living together in one household. The child support amount is not just about what the non-residential parent owes — it reflects what both parents are each expected to contribute to the child’s needs.

The Montana guidelines are set out in ARM Title 37, Chapter 62, Subchapter 1 (rules ARM 37.62.101 through 37.62.148). These rules are administered by Montana’s Child Support Services Division (CSSD) of the Department of Public Health and Human Services. The guidelines must be reviewed at least once every four years under MCA § 40-5-209. The next scheduled review is December 2028.

One important legal note: Both the District Court and CSSD are required to use the guidelines in every child support proceeding — contested, uncontested, and default cases alike (ARM 37.62.101). The guidelines create a rebuttable presumption (ARM 37.62.102) — meaning the amount they produce is presumed to be correct, but either parent can present evidence to argue it should be adjusted up or down based on the child’s specific needs and circumstances.

The Montana Child Support Formula: Step by Step

The full calculation has eight main steps. Here is what happens at each one.

Step 1: Determine Each Parent’s Gross Income

The starting point is each parent’s gross income from all sources — before any deductions. Under ARM 37.62.105, income for child support is broadly defined. It includes virtually every form of economic benefit a parent receives:

• Wages, salaries, tips, commissions, bonuses
• Self-employment income (gross receipts minus ordinary and necessary business expenses)
• Dividends, interest, capital gains, royalties, trust income
• Pension payments and periodic distributions from retirement accounts
• Social Security benefits (except SSI and certain disability-based benefits)
• Veterans’ benefits (except means-tested benefits)
• Workers’ compensation and disability payments
• Unemployment benefits
• Alimony or spousal maintenance received from a prior relationship
• Non-cash benefits — personal use of a company vehicle, employer-provided housing, free utilities
• Draws or advances against wages
• Grants, scholarships, and financial subsidies not required to be repaid

What is not counted as income (ARM 37.62.105(3)):

• Income of a new spouse or domestic partner in the parent’s household
• Means-tested public assistance (TANF, SNAP, SSI)
• Child support payments received from other relationships
• Adoption subsidies (unless the subsidized child’s expenses are in the calculation)

For voluntary overtime: if a parent works voluntary overtime and those earnings are expected to continue, they are presumed to be available for child support — subject to rebuttal (ARM 37.62.105(5)).

Step 2: Imputed Income — When a Parent Is Not Working to Full Capacity

One of the most important rules in Montana child support: parents cannot simply quit their jobs, work fewer hours, or underperform to reduce their child support obligation.

Under ARM 37.62.106, Montana can impute income to a parent — meaning the court assigns them an income figure based on what they are capable of earning, not just what they actually earn — when:

• The parent is unemployed
• The parent is underemployed (working less than full time when full-time work is available, or earning less than they are qualified to earn)
• The parent fails to provide sufficient proof of income
• The parent’s employment status is unknown
• The parent is a student

Montana’s rules presume that every parent is capable of working at least 40 hours per week at minimum wage (ARM 37.62.106(1)). If you want to rebut that presumption, you need actual evidence — not just a claim that work isn’t available.

Imputed income is based on a realistic assessment of what the parent could earn, considering their work history, education, qualifications, local job market, health, and other relevant factors (ARM 37.62.106(3)).

Exceptions — when income cannot be imputed (ARM 37.62.106(6)):

• The cost of childcare for dependents in the parent’s household would substantially offset imputed income
• The parent has a physical or mental disability preventing them from earning income
• The parent is incarcerated for more than 180 days
• A legal dependent in the household has unusual physical or emotional needs requiring the parent’s presence at home
• The parent has made diligent efforts to find suitable work and been unsuccessful

Step 3: Subtract Allowable Deductions

From each parent’s gross income, certain deductions are allowed before calculating their share of child support. Under ARM 37.62.110, allowable deductions include:

• Actual income tax liability (federal and Montana state)
• Social Security taxes (FICA and Medicare)
• Alimony or spousal maintenance paid under a court or administrative order
• Child support paid under existing orders for other children from different relationships
• Health insurance premiums paid under a court order for children from other relationships
• Mandatory contributions to IRS-approved retirement and deferred compensation plans (fully deductible)
• Actual unreimbursed employment-related expenses (uniforms, tools, union dues, license fees, business vehicle use)
• Extraordinary unreimbursed medical expenses for the parent (to maintain their health or earning capacity)
• Student loan interest for post-secondary education that has resulted in an economic benefit to the children of this calculation
• For children of another relationship who live with the parent: half of the primary child support allowance for those children

What is not deductible (ARM 37.62.111):

• Credit union payments, savings deductions, or other voluntary payroll deductions
• Expenses incurred supporting a spouse who is capable of self-support
• Bankruptcy payments (except for those representing otherwise deductible debts)
• Costs associated with a stepchild

Step 4: Subtract the Personal Allowance

After allowable deductions, Montana subtracts a Personal Allowance from each parent’s income. This is designed to protect a minimum level of financial resources for each parent themselves before calculating what they owe for child support.

Under ARM 37.62.114, the personal allowance equals 1.3 times the federal poverty guideline for a one-person household, updated annually. The personal allowance increases if the parent has legal dependents in their household whose needs have not otherwise been accounted for in the calculation.

The result — gross income minus deductions minus personal allowance — is called each parent’s Income Available for Child Support (ARM 37.62.116).

Step 5: Determine Each Parent’s Share of the Combined Income

Both parents’ Incomes Available for Child Support are added together to get the Total Combined Income (ARM 37.62.118). Then each parent’s individual income is divided by the combined total to determine their proportional share.

For example: if Parent A has $2,000 available and Parent B has $1,000 available, the combined total is $3,000. Parent A’s share is 67%. Parent B’s share is 33%.

This percentage determines each parent’s share of every support obligation: the base support, childcare costs, health insurance, and medical expenses.

Step 6: Calculate the Primary Child Support Allowance

The Primary Child Support Allowance (ARM 37.62.121) is the base amount that covers a child’s food, shelter, clothing, and related daily needs. It is calculated as a percentage of the Personal Allowance:

• First child: 30% of the Personal Allowance
• Second child: add 20% of the Personal Allowance
• Third child: add another 20% of the Personal Allowance
• Each additional child beyond three: add 10% of the Personal Allowance per child

Each parent contributes to this allowance proportionally — based on the income share percentage calculated in Step 5.

Step 7: Add Supplements to the Primary Allowance

On top of the primary child support allowance, additional supplement amounts are added for specific actual costs (ARM 37.62.123):

• Childcare costs: Reasonable costs of childcare required as a prerequisite for either parent to work, reduced by the applicable federal dependent care tax credit
• Health insurance: The actual cost of adding the children to an existing health insurance policy, or the cost of a child-only policy
• Unreimbursed medical expenses: Health care costs for the children that exceed $250 per year, per child, and are recurring and predictable
• Other needs: Any other specific needs of the child determined by the circumstances of the case

Like the primary allowance, these supplements are shared proportionally between the parents based on their income shares. Each parent receives credit for any supplements they are already paying directly.

Step 8: Apply the Standard of Living Adjustment (SOLA)

Montana’s child support formula includes something most people have never heard of: a Standard of Living Adjustment (SOLA) (ARM 37.62.128). The purpose of SOLA is to ensure that a child benefits from a parent’s higher income — not just at a basic subsistence level.

After calculating the primary allowance and supplements, if a parent has income remaining after their personal allowance and their share of the child support obligation, that remaining income is subject to SOLA. SOLA is calculated by multiplying that remaining income by a factor that depends on the number of children:

SOLA is one of the features of Montana’s formula that surprises high-income parents the most. It means that higher-earning parents pay more than just the basic formula amount — the child’s standard of living should, to the extent possible, reflect both parents’ financial capacity.

How Parenting Time Affects Child Support

Parenting time is one of the most significant variables in Montana’s child support formula. Under ARM 37.62.124, the key threshold is 110 overnight days per year.

A “day” under the guidelines (ARM 37.62.124) is defined as the majority of a 24-hour calendar period in which the child is with or under the control of a parent. When a child is at school or daycare, the parent who is the primary contact for that provider is the parent who counts that time.

The adjustment for more than 110 overnights is calculated by recalculating each parent’s obligation proportionally based on the residential schedule — allocating support costs to the time the child spends with each parent, then offsetting the two obligations against each other. The parent with the higher remaining obligation pays a transfer payment to the other parent (ARM 37.62.134).

The practical takeaway: More parenting time generally means a lower child support payment. But pursuing more parenting time primarily to reduce child support is a poor strategy — courts evaluate parenting plan arrangements based on the child’s best interests, not on the financial implications for either parent. An attorney can help you understand how your specific parenting schedule affects your support obligation.

The Transfer Payment: What One Parent Pays the Other

After all of the above calculations are done for each parent separately, Montana offsets the two obligations against each other. The parent with the higher obligation pays the difference — called the transfer payment — to the other parent (ARM 37.62.134).

When all children reside primarily with one parent and the other parent has fewer than 110 overnight days, the transfer payment equals the non-residential parent’s full calculated obligation. When there is significant shared parenting time (more than 110 days), the obligations are offset as described above.

Child support is paid in U.S. dollars — not in gifts, clothing, food, direct payments to the child, or other in-kind contributions (ARM 37.62.142). In-kind contributions do not count toward your child support obligation unless specifically ordered by the court.

The Minimum Support Obligation

No parent’s obligation falls to zero simply because their income is very low. Under ARM 37.62.126, Montana sets a minimum support obligation for all parents. The specific amount depends on the parent’s income after deductions relative to their personal allowance:

• If a parent’s income after deductions is more than their personal allowance, their minimum contribution is 12% of their income after deductions.
• If a parent’s income after deductions is less than or equal to their personal allowance, a sliding scale table applies (ARM 37.62.126(3)) — the minimum contribution can range from $0 (for very low income ratios) up to about 11% of income after deductions.

The minimum obligation can be rebutted based on the specific circumstances of a case — but there must be an appropriate finding on the record to support any deviation from it.

Key Additional Rules That Affect Your Calculation

Long Distance Parenting Adjustment

If a parent travels more than 2,000 miles per year to exercise their parenting time under the parenting plan, they may be entitled to a Long Distance Parenting Adjustment under ARM 37.62.130. The adjustment reduces the income available for SOLA by the amount that actual long-distance transportation costs exceed 2,000 miles multiplied by the current IRS business mileage rate. This adjustment covers transportation costs only — not meals, lodging, or other expenses.

Social Security and Veterans Benefits

Under ARM 37.62.144, when a child receives Social Security or Veterans’ benefits based on a parent’s earnings or service record:

• Those benefits are not included in the parent’s income
• If the child’s monthly benefit equals or exceeds the parent’s calculated child support obligation, that obligation is considered satisfied
• If the benefit is less than the obligation, the parent pays only the difference
• Lump sum benefit payments are credited to the parent’s obligation for the months they accumulated

Anticipated Changes

Under ARM 37.62.140, if any material change in circumstances is anticipated within 18 months (such as a child reaching a certain age, a parent completing school, or a change in employment), the court must calculate support separately for both the current situation and the anticipated future situation. The order then automatically adjusts to the future amount when the anticipated change occurs, reducing the need for future modification proceedings.

Overtime Income

If overtime is mandatory and the worker has no control over it, overtime earnings are included in income for child support. If overtime is voluntary but expected to continue for the foreseeable future, it is also presumed to be available for child support — subject to rebuttal with evidence (ARM 37.62.105(5)).

Self-Employment Income

For self-employed parents, income is calculated as gross receipts minus reasonable and necessary business expenses (ARM 37.62.105(2)(b)). Business losses from one entity cannot be used to offset income from an unrelated business. Net losses from one business generally cannot reduce other income — except for closely related businesses where the loss genuinely offsets profits in the related enterprise.

Can the Guideline Amount Be Changed?

Yes. The guidelines create a rebuttable presumption — meaning the calculated amount is assumed to be correct, but it can be challenged. Under ARM 37.62.102, either parent can request a variance from the guideline amount based on the specific needs of the child and the circumstances of the family. If the court grants a variance, the order must include a specific written finding explaining why the guideline amount would be unjust or inappropriate.

Common grounds for requesting a variance include:

• Extraordinary medical, educational, or therapeutic needs of the child that the standard formula does not capture
• Significant income fluctuations that make the calculated amount unrealistic
• A high-income parent where the calculated amount would far exceed the child’s actual needs
• A parent with multiple children from different relationships where the combined obligations would create genuine hardship

Any agreement between parents to deviate from the guideline amount must be in writing, include an explanation of why the guideline amount would be unjust, state what the guideline amount would have been, and be approved by the court (ARM 37.62.102(5)).

How Is Child Support Modified in Montana?

Once a child support order is in place, it can be modified. Under MCA § 40-4-208, a court may modify a child support order when there has been a significant change in circumstances — typically defined as a change that would result in at least a 15% difference in the current monthly obligation under the guidelines. Common reasons for modification include:

• A substantial increase or decrease in either parent’s income
• A significant change in the child’s medical or childcare costs
• A change in the parenting time schedule that crosses the 110-day threshold
• A parent becomes unemployed, disabled, or incarcerated
• The child’s circumstances change significantly (new special needs, change of school, etc.)

Child support orders established through CSSD are also subject to review every three years — either parent can request a review without showing a change in circumstances (MCA § 40-5-993). Court-ordered support requires a modification motion filed with the district court.

Who Enforces Child Support in Montana?

Montana has multiple enforcement mechanisms for unpaid child support:

• Income withholding: Under MCA § 40-4-204, child support orders automatically include income withholding provisions. Your employer deducts child support directly from your paycheck and sends it to the appropriate account.
• CSSD enforcement: Montana’s Child Support Services Division (CSSD) can enforce child support orders through license suspension, tax refund interception, contempt proceedings, and other administrative tools. CSSD can be reached at 1-800-346-KIDS (1-800-346-5437).
• Contempt of court: Willful failure to pay court-ordered child support is contempt. Courts can impose fines and, in serious cases, jail time for persistent non-payment.
• Credit reporting: Significant arrears can be reported to credit bureaus.
• Passport denial: Federal law bars issuance of a U.S. passport to parents who owe more than $2,500 in child support arrears.

Child support and parenting time are legally separate in Montana. A parent cannot withhold child support because they are being denied parenting time, and a parent cannot deny parenting time because the other parent is not paying support. Both obligations are independent rights of the children — not leverage tools for either parent.

A Practical Example of How the Calculation Works

Hypothetical situation: Two parents, one child. Parent A earns $4,000/month gross. Parent B earns $2,000/month gross. Parent B has primary parenting time; Parent A has 90 overnights per year (under 110, so no parenting time adjustment).

Combined gross income: $6,000/month

Parent A’s share: $4,000 ÷ $6,000 = 67%

Parent B’s share: $2,000 ÷ $6,000 = 33%

After deductions and personal allowances are subtracted from each parent’s income (which would reduce these numbers), each parent’s share of the primary child support allowance and supplements is determined proportionally. Then SOLA is applied to any remaining income.

The result is each parent’s total support obligation. Since Parent B is the primary residential parent, Parent A pays a transfer payment to Parent B representing the portion of the children’s costs that Parent A is responsible for.

Why the exact numbers matter: Small differences in income, deductions, parenting days, healthcare costs, and childcare costs can meaningfully change the final support number. The only way to know your actual obligation is to run the full calculation using the official Montana Child Support Guidelines worksheet — which your attorney or CSSD can do for your specific situation.

How S. DeBoer Attorney at Law Helps Missoula Families With Child Support

Child support calculations in Montana are more complex than most people realize going in. The formula involves multiple layers — income determination, imputed income challenges, deduction analysis, parenting time counts, supplement calculations, and SOLA — and each layer involves judgment calls that can meaningfully affect the final number.

Stephanie DeBoer and her team at S. DeBoer Attorney at Law have handled child support matters in Missoula for more than 15 years. Whether you are establishing support for the first time, responding to a motion to modify, challenging an imputed income figure, or trying to understand whether your current order accurately reflects the law, the firm can help you navigate the calculation and advocate for an outcome that is fair to you and your children.

Stephanie is a Montana native and Alexander Blewett III School of Law graduate (2010 Juris Doctorate) who has practiced family law in Missoula since her graduation. The firm’s team includes attorney Shelley, who has more than 20 years of family law experience and is licensed in both Montana and Alabama; Kathleen, who clerked for a Montana District Court judge; Nico, who brings careful attention to detail and client-focused advocacy; and Katy, a former U.S. Marine and UM law graduate focused on helping families navigate difficult circumstances with clarity and confidence.

“[ INSERT REAL CLIENT QUOTE HERE — ideal: a parent who felt the firm helped them achieve a fair child support outcome, whether establishing an order or modifying an existing one. Format: First Name L., Missoula, MT ]”

Frequently Asked Questions

Does Montana use a percentage of income for child support?

No. Montana does not use a simple percentage-of-income model. It uses the Income Shares Model under ARM Title 37, Chapter 62, which considers both parents’ incomes, personal allowances, allowable deductions, childcare costs, health insurance, parenting time, and a Standard of Living Adjustment. The calculation is more complex than a single percentage — and more tailored to the financial reality of each family. The official Montana Child Support Guidelines worksheet must be used in every proceeding.

What if one parent is unemployed or quits their job?

Montana can impute income to a parent who is unemployed or underemployed under ARM 37.62.106. The rule presumes every parent is capable of working 40 hours per week at minimum wage, at a minimum. If a parent voluntarily reduces their income to try to lower child support, the court can base the calculation on what they are capable of earning rather than what they are actually earning. There are exceptions for parents who are genuinely disabled, incarcerated for more than 180 days, or facing other documented barriers to employment — but those exceptions require evidence.

Does child support change if parenting time changes?

Yes. Parenting time is a direct factor in Montana’s child support formula. The key threshold is 110 overnight days per year under ARM 37.62.124. If the non-residential parent has fewer than 110 overnights, there is no parenting-time adjustment and they pay their full calculated obligation. If they have 110 or more overnights, the transfer payment is adjusted to account for direct costs they incur while the child is in their care. A significant change in parenting time is also grounds for requesting a modification of an existing child support order.

Can parents agree to a different amount than what the guidelines say?

Yes, but with important conditions. Under ARM 37.62.102, any agreement to deviate from the guideline amount must be in writing, must include a specific explanation of why the guideline amount would be unjust or inappropriate, must state what the guideline amount would have been, and must be approved by the court. A private agreement between parents to pay a different amount — without court approval — is not legally enforceable, and arrears continue to accumulate based on the official court order.

Does my new spouse’s income count toward my child support obligation?

No. Under ARM 37.62.105(3)(a), income of a subsequent spouse or domestic partner in a parent’s household is explicitly excluded from income for child support purposes. Child support is calculated based solely on the legal parents’ incomes, not on who they may have since married or partnered with.

How often can child support be modified in Montana?

Court-ordered child support can be modified when there has been a significant change in circumstances. Generally, this means a change that would result in at least a 15% difference in the calculated monthly obligation. There is no minimum time between modification requests, though courts do look skeptically at frequent, repeated modification motions. Child support orders established through CSSD can be reviewed every three years by either parent without needing to show a change in circumstances.

What happens if I don’t pay child support in Montana?

The consequences are serious and escalate with the length of non-payment. Montana’s enforcement tools include automatic income withholding directly from your paycheck (MCA § 40-4-204), CSSD administrative enforcement, contempt of court proceedings with potential fines and jail time, state and federal tax refund interception, professional and driver’s license suspension, credit bureau reporting, and denial of a U.S. passport for arrears over $2,500. Child support arrears do not go away — they accumulate with interest and cannot be discharged in bankruptcy. If you are struggling to pay, the right step is to file for a modification as soon as possible — not to stop paying and hope the situation resolves itself.

Is child support taxable in Montana?

No. Under federal tax law, child support payments are not deductible by the parent who pays them and are not taxable income for the parent who receives them. This differs from spousal maintenance (alimony), which has different tax treatment. Montana follows federal tax law on this point. If tax issues related to your child support arrangement are complex — particularly for self-employed parents or those with significant non-wage income — consulting with both a family law attorney and a tax professional is advisable.