Montana Alimony Calculator 2026
Montana has no alimony formula: a judge decides the amount and the length. This page explains what the law says and shows a clearly labelled illustration from both incomes and the length of the marriage. Everything runs privately in your browser, with no sign-up.
Not legal advice — a court decides. Montana has no alimony formula. A judge decides whether to award maintenance, how much and for how long; the figure below is an illustration, not a prediction.
Montana Alimony Formula & Factors
Montana has no alimony formula. Mont. Code Ann. § 40-4-203 allows maintenance only if the spouse asking lacks sufficient property for reasonable needs and cannot be self-supporting through appropriate employment, or has custody of a child whose circumstances make outside work inappropriate. The amount and period are what the court considers just, without regard to marital misconduct, after considering that spouse's financial resources, the time needed for education or training, the standard of living, the length of the marriage, the spouse's age and physical and emotional condition, and the other spouse's ability to pay.
What the Illustrative Estimate Is
Because Montana law gives no figure to calculate, the dollar amount on this page is an illustration only. It uses the reference method recommended by a commission of the American Academy of Matrimonial Lawyers (AAML) and adopted by its Board of Governors in March 2007: 30% of the payor's gross income minus 20% of the recipient's gross income, limited so that the recipient ends up with no more than 40% of the couple's combined gross income. The method is set out in Mary Kay Kisthardt's article in the Journal of the American Academy of Matrimonial Lawyers (vol. 21, 2008) and summarised by Maryland's highest court in Boemio v. Boemio (2010).
The AAML method is not Montana law and Montana courts are not bound by it. It lists its own reasons to depart from the result, such as a spouse caring for a young or disabled child, age or health, or a career given up for the other spouse. It was written when alimony was still tax-deductible for the payer, and it does not apply when combined gross income is above $1,000,000 a year. Treat the figure as a starting point for a conversation with a lawyer, not as a prediction.
Montana Alimony Rules at a Glance
| Point | Montana rule | Source |
|---|---|---|
| Amount | No formula; decided by the court | Mont. Code Ann. § 40-4-203 |
| Length | No schedule; decided by the court | Mont. Code Ann. § 40-4-203 |
| Figure shown on this page | An illustration using the AAML reference method (30% of payor gross income − 20% of recipient gross income, limited to 40% of combined income) — not Montana law | AAML Commission recommendations (2007) |
| Who decides | A judge, on the evidence in the case | Mont. Code Ann. § 40-4-203 |
| Federal income tax | Not deductible by the payer and not income to the recipient for agreements executed after 2018 | IRS Topic No. 452 |
Worked Example: Montana Alimony Calculator
Take gross incomes of $8,000 and $3,000 a month. Under the AAML reference method, 30% of $8,000 is $2,400 and 20% of $3,000 is $600, a difference of $1,800. The limit is 40% of the combined $11,000, which is $4,400, less the recipient's own $3,000: $1,400. The illustrative amount is the lower figure, $1,400 a month ($16,800 a year). This is an illustration, not an amount set by Montana law.
For a 12-year marriage the same reference method multiplies the length by 0.75, giving about 9 years. That too is an illustration; Montana law sets no schedule.
These are the figures the calculator shows when the page first loads. A real order depends on evidence a calculator cannot see.
Montana Alimony Duration Rules
Montana law sets no schedule for how long maintenance lasts; the court fixes the period case by case.
The duration this page shows is an illustration only. It uses the same AAML reference method: the length of the marriage multiplied by 0.3 for marriages of up to 3 years, 0.5 for more than 3 and up to 10 years, and 0.75 for more than 10 and up to 20 years, with open-ended support suggested after more than 20 years.
Is Alimony Taxable in Montana?
For federal income tax, alimony or separate maintenance paid under a divorce or separation agreement executed after 2018 is not deductible by the payer and is not included in the recipient's income. Payments under an agreement executed before 2019 are generally still deductible by the payer and taxable to the recipient, unless the agreement was later modified and the modification expressly adopts the new rule (IRS Topic No. 452). Child support is never deductible and is not income.
This page does not cover Montana state income tax. State rules are set separately and can differ from the federal rule, so check with the state tax agency or a tax adviser.
Modifying Montana Alimony
Whether an order can be changed depends on its wording and on the type of support. In most cases either spouse can ask the court to modify periodic payments after a substantial change in circumstances, unless the decree or the spouses' agreement makes the support non-modifiable.
Read the order itself and Mont. Code Ann. § 40-4-203 before relying on a general rule, and get advice from a family lawyer licensed in Montana about your own case. Nothing on this page is legal advice.
Last updated: October 2026. Sources: Mont. Code Ann. § 40-4-203 (Montana Legislature); AAML Commission recommendations (Kisthardt, 21 J. Am. Acad. Matrim. Law. 61); IRS Topic No. 452.
Frequently Asked Questions
How is alimony calculated in Montana?
Montana has no alimony formula. Mont. Code Ann. § 40-4-203 allows maintenance only for a spouse who lacks sufficient property and cannot be self-supporting, in an amount the court considers just after weighing six factors, without regard to marital misconduct. The amount on this page is an illustration using the AAML reference method, not Montana law.
Does Montana use a formula for alimony?
No. Mont. Code Ann. § 40-4-203 sets no percentage, cap or schedule for maintenance, so the judge decides the amount and the length case by case. Any calculator can only illustrate; this one uses the method published by the American Academy of Matrimonial Lawyers, which Montana courts are not bound by.
How long does Montana alimony last?
Montana law sets no fixed schedule; the court sets the period case by case. The duration this page shows is an illustration using the AAML reference method (a fraction of the length of the marriage), not Montana law.
Can Montana alimony be modified?
It depends on the order. In most cases either spouse can ask the court to modify periodic payments after a substantial change in circumstances, unless the decree or the spouses' agreement makes the support non-modifiable. Check the wording of your order and Mont. Code Ann. § 40-4-203 before relying on a general rule.
Is alimony taxable in Montana?
For federal income tax, alimony paid under a divorce or separation agreement executed after 2018 is not deductible by the payer and is not income to the recipient (IRS Topic No. 452). Agreements executed before 2019 generally keep the old treatment, deductible by the payer and taxable to the recipient, unless a later modification expressly adopts the new rule. This page does not cover Montana state income tax, which is set separately.