How to Calculate Child Support in Idaho: Income, Steps, Custody

To calculate child support in Idaho, you combine both parents’ monthly incomes, look up the basic support obligation on the schedule in Idaho Rule of Family Law Procedure 120, and divide that obligation between the parents in the same ratio as their incomes. Health insurance premiums and work-related childcare get added on and split the same way, and a shared-custody formula kicks in once a child spends more than 25% of overnights with each parent. The number the worksheet produces is legally presumed correct, so the calculation is the order unless a judge finds a reason to deviate.¹

Idaho uses an income shares model. The theory is that the court should estimate what the parents would have spent on the child together and then split that cost in proportion to what each parent earns. The schedule in IRFLP 120 applies graduated percentages to combined income brackets: for one child, roughly 18% on the first $10,000 of combined annual income down to 5% at higher brackets, with higher percentages for two or more children, up to five. The schedule tops out at $440,000 in combined annual Guidelines Income; above that, the court calculates on the first $440,000 and then looks at the child’s needs, the standard of living, and each parent’s resources to decide whether to add more.¹

What Counts as Income

Idaho defines gross income broadly. It includes wages, salaries, commissions, bonuses, dividends, pensions, interest, trust income, annuities, Social Security benefits, workers’ compensation, unemployment insurance, disability insurance, alimony received, veteran’s benefits, and education grants or scholarships. Public assistance the parent receives is also included, except in cases of extraordinary hardship. Child support a parent receives for a different child is presumed spent on that child and is not counted as the parent’s income.¹

Overtime and Second-Job Pay

Overtime and second-job earnings are not automatically counted. The court can exclude them only when all five of these conditions are true: the overtime is not a condition of employment or the second job is voluntary; the extra work is part-time or paid hourly; the parent did not change jobs to manipulate the calculation; the parent already works full-time at least 48 weeks a year; and current income already covers the support obligation. Miss one condition and the extra income goes in.¹

Self-Employment and Business Income

For self-employed parents and those with rental or royalty income, gross income is gross receipts minus the ordinary and necessary expenses of the business. The court reviews those expenses independently and can disallow any it finds unnecessary, so the figure used for child support can differ from what appears on a tax return. Two deductions are allowed by default: straight-line depreciation over the asset’s life, and one-half of the self-employment Social Security tax paid on business income.¹

Imputed Income

If a parent is voluntarily unemployed or underemployed, the court can base support on what that parent could be earning. Idaho calls this “potential income” and sets it by looking at the parent’s work history, qualifications, and local job opportunities. Income is generally not imputed to a parent who is physically or mentally incapacitated.¹

Deductions That Reduce Gross Income

Before you reach the schedule, you subtract certain obligations from each parent’s gross income. What’s left is that parent’s Guidelines Income.¹

Child support or spousal maintenance ordered in another case.
Spousal maintenance awarded in the current case.
Voluntary support actually being paid, on a consistent pattern, for a child from another relationship, even without a court order.
A deduction for a biological or adopted child from another relationship living in the parent’s home, equal to the guideline amount for that child using only that parent’s income.

One limit matters in modification cases: children born or adopted after the original order was entered do not count. A parent cannot shrink an existing obligation by having more children.¹

The Six Steps of the Calculation

Idaho publishes an official worksheet and a free online calculator at online.idchildsupport.com. The math it runs looks like this:

Figure each parent’s gross monthly income from pay stubs, tax returns, W-2s, 1099s, and any other sources. Convert everything to a monthly figure.
Subtract the allowable deductions from each parent’s gross income. The result is each parent’s Guidelines Income.
Add both parents’ Guidelines Income together.
Look up the basic monthly support obligation on the IRFLP 120 schedule using combined Guidelines Income and the number of children.
Calculate each parent’s share of the combined income as a percentage, and apply that percentage to the basic obligation. If Parent A earns $4,000 and Parent B earns $6,000, Parent A owes 40% of the basic obligation and Parent B owes 60%.
Add the children’s health insurance premiums and work-related childcare, split in the same percentages, to each parent’s share.

The final figure is the presumptive child support amount. The parent without primary physical custody typically pays their share to the other parent; the custodial parent is presumed to spend their own share directly on the child.¹

Shared Custody Changes the Formula

Once a child spends more than 25% of overnights per year with each parent, Idaho treats the arrangement as shared physical custody and adjusts for the cost of running two homes. The basic obligation is multiplied by 1.5. Each parent’s income-share percentage is then multiplied by the percentage of time the child spends with the other parent. The two numbers are offset, and the parent with the larger figure pays the difference.¹

Two guardrails apply. No parent pays more under the shared-custody formula than they would under the straight calculation. And if the formula still shows the parent who has the child more than half the overnights owing support, that parent can challenge the result using the deviation factors below.¹

Health Insurance, Childcare, and Big Medical Bills

The premium cost of the children’s health insurance and any work-related childcare are split between the parents in the same proportions as the basic obligation and added to the monthly order.¹

Uninsured medical expenses are handled separately. Any course of treatment that will exceed $500 requires advance written approval from both parents or a prior court order. If a parent incurs a large expense without approval, the court can still grant relief under extraordinary circumstances and has discretion to split the cost in different proportions than the standard order. A parent who unreasonably withholds consent may end up with a less favorable split.¹

When a Judge Can Deviate

The guideline number is presumed correct, but a judge can order a different amount when the evidence shows the standard calculation would produce an inappropriate result. The court has to state the guideline figure on the record and explain why it is departing from it. Factors that can justify deviation include the child’s own financial resources, each parent’s financial circumstances, the child’s standard of living during the marriage, and any special physical, emotional, or educational needs.¹

At the low end, the guidelines rarely set support at zero. When the paying parent’s monthly income is below $800, the court looks at both parents’ incomes and living expenses to find the most the paying parent can handle without dropping below basic self-support. Even then, there is a rebuttable presumption that support should be at least $50 per month per child.¹

Tools and When to Get Help

The state’s online calculator at online.idchildsupport.com runs the IRFLP 120 formulas and gives a quick estimate once you enter both parents’ income figures and the number of children. The Idaho Department of Health and Welfare’s Child Support Services can help establish or modify an order when you apply for their services, and the application forms are on the department’s website. Relatives and third-party caretakers with legal or physical custody can apply as well.²

If your situation involves business ownership, multiple income streams, disputed overtime, or a shared-custody schedule, working through the worksheet with a family law attorney is usually worth the cost. Judges scrutinize self-employment deductions closely, and small categorization errors can swing the monthly number by hundreds of dollars.

1
Idaho Supreme Court. IRFLP 120 – Idaho Child Support Guidelines
2
Idaho Department of Health and Welfare. Child Support Enforcement Services