Montana child support calculator

Montana starts from the opposite end to most states. Rather than asking what a family at a given income spends on children, it asks what each parent needs to live on first: a personal allowance of $20,748 a year comes off the top, and only what remains is income available for child support. The children’s allowance is then divided in proportion to that available income — so a parent earning barely above their own allowance contributes very little, and the split is far more progressive than a straight income-shares percentage.

There is no schedule to look up. Montana’s dollar inputs are two short figures that CSSD republishes annually from the federal poverty guidelines: the personal allowance of $20,748 a year for each parent, and the primary child support allowance — $6,224 a year for one child, rising to $24,897 for eight. The current tables took effect on 1 February 2026. Because the whole calculation rests on a handful of numbers rather than a thousand-row table, it is unusually easy to check and unusually easy to get out of date.

Covering basic needs is only the first half. Once the paying parent’s share of the children’s allowance is met, the SOLA adds a percentage of whatever income that parent still has available — 14% for one child, 21% for two, 27% for three, rising to 47% for eight or more. It is what stops the formula capping children at subsistence when a parent earns well. Child care net of the dependent-care tax credit, health-insurance premiums and unreimbursed medical costs over $250 a child are added to the children’s allowance before the split. Where a parent’s income after deductions is at or below the personal allowance, Worksheet C substitutes a minimum contribution — a percentage of income that climbs with the ratio of income to allowance.

Montana counts days, and the threshold is 110. Where every child lives primarily with one parent and spends 110 days or fewer a year with the other, Worksheet A’s annual figure simply divides by twelve — the case this calculator runs. Past that, or where the children are split between homes, Montana moves to Worksheet B, which works out each child’s support separately by the days spent with each parent and nets the two obligations against each other.

It runs Worksheet A: personal allowance, income available for support, the children’s allowance and supplement, the proportional split, the SOLA, and the Worksheet C minimum where it applies. It does not compute income after deductions from your pay stubs, run Worksheet B for shared or split parenting, apply the Worksheet D long-distance parenting adjustment, deduct an allowance for other children you support, or credit supplemental expenses the paying parent pays directly — the supplement entered here is treated as paid by the other parent. For a figure you can file, use the CSSD worksheets or consult an attorney.