How Idaho child support is calculated
Idaho’s Child Support Guidelines are court rule I.R.F.L.P. 120, amended effective July 1, 2025. They use an income shares model: support is set from both parents’ incomes combined, then divided between them in proportion to income.
1. Guidelines Income
Start with each parent’s gross income from any source: wages, salary, commissions, bonuses, business income, interest, pensions, social security and other benefits, alimony received, and more I.R.F.L.P. 120(e)(1)(A). Business income is receipts minus ordinary and necessary expenses, straight-line depreciation and one-half of self-employment tax I.R.F.L.P. 120(e)(1)(C). Significant employment benefits such as a company car or housing count I.R.F.L.P. 120(e)(2), and a parent who is voluntarily unemployed or underemployed can be assigned potential income I.R.F.L.P. 120(e)(3).
From gross income, subtract I.R.F.L.P. 120(f):
- child support or spousal maintenance ordered in another case;
- spousal maintenance ordered in this case;
- a shown pattern of support paid without an order for a child of another relationship;
- for each child of another relationship living in the parent’s home, the guideline support for that child computed from that parent’s income alone. The rule’s example: a parent earning $1,800 a month deducts $312, leaving $1,488.
2. The basic obligation
Add both parents’ annual Guidelines Income. The schedule applies a percentage to each slice of that combined income, like tax brackets, and the sum is the basic obligation for all the children I.R.F.L.P. 120(i)(1):
| Combined annual Guidelines Income | 1 child | 2 children | 3 children | 4 children | 5 children |
|---|---|---|---|---|---|
| First $10,000 | 18% | 26% | 30% | 33% | 36% |
| $10,000 – $20,000 | 17% | 25% | 29% | 32% | 35% |
| $20,000 – $30,000 | 15% | 23% | 27% | 30% | 33% |
| $30,000 – $40,000 | 14% | 22% | 26% | 29% | 32% |
| $40,000 – $50,000 | 13% | 20% | 24% | 27% | 30% |
| $50,000 – $70,000 | 12% | 17% | 20% | 22% | 24% |
| $70,000 – $90,000 | 9% | 13% | 16% | 18% | 20% |
| $90,000 – $110,000 | 6% | 9% | 12% | 14% | 16% |
| $110,000 – $130,000 | 5% | 8% | 11% | 13% | 15% |
| $130,000 – $150,000 | 5% | 8% | 11% | 13% | 15% |
| $150,000 – $440,000 | 5% | 8% | 11% | 13% | 15% |
The rule also prints per-month and per-year dollar columns. In its last row, the dollar figure is the running total through $150,000 (for example $15,100 for one child), not the amount for that slice; the percentages are what the schedule applies.
The schedule stops at combined income of $440,000 a year. Support on that amount is calculated normally, and the court may award more after considering factors such as the child’s needs and the standard of living during the marriage I.R.F.L.P. 120(i)(7). The schedules for five children are not a limit for larger families I.R.F.L.P. 120(i)(2).
3. Each parent’s share
Each parent is responsible for the basic obligation in proportion to their Guidelines Income I.R.F.L.P. 120(c)(1). If one parent earns 70% of the combined income, their share is 70% of the basic obligation.
4. Custody: who pays whom
Custody is measured in overnights per calendar year I.R.F.L.P. 120(i)(3)(A). Every other weekend is 52 overnights, or about 14%.
- Primary custody. When one parent has 25% or fewer of the overnights, that parent pays their share to the other I.R.F.L.P. 120(i)(3)(B).
- Shared custody. When each parent has more than 25%, the basic obligation is multiplied by 1.5, divided by income, and each parent’s amount is multiplied by the time the children spend with the other parent; the larger amount pays the difference I.R.F.L.P. 120(i)(4). See shared custody in detail →
- Split custody. When each parent has at least one child living primarily with them, support is calculated per child with the 1.5 multiplier for an equal number of children in each home, then offset I.R.F.L.P. 120(i)(6).
5. Adjustments
Work-related child care, the children’s health insurance premium, uncovered medical costs, the federal and Idaho tax benefit for claiming the children, and dependency benefits from a parent’s disability or retirement are handled separately I.R.F.L.P. 120(g). How each adjustment works →
Floors and limits
- Support should rarely be zero. There is a rebuttable presumption of at least $50 per child per month, and when the paying parent’s income is under $800 a month the court should review incomes and living expenses carefully I.R.F.L.P. 120(c)(4).
- The court can depart from the guidelines when evidence shows the amount is inappropriate, stating the guidelines amount and the reasons on the record I.R.F.L.P. 120(b)(3).
How long support lasts
Support runs until 18, or up to 19 while a child is pursuing a high school education I.R.F.L.P. 120(a). The judgment states support for all the children and the amount due for the remaining children as each one ages out. Each step is recalculated from the schedule for the smaller number of children, not reduced proportionally I.R.F.L.P. 120(j).
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Source: Idaho Rules of Family Law Procedure, Rule 120 (Idaho Supreme Court).