Child Support Calculations in Idaho

Idaho uses the Income Shares model under Idaho Rules of Family Law Procedure (IRFLP) Rule 120, effective July 1, 2025. Whether you're navigating an uncontested or contested divorce, understanding Idaho's unique features—including the 25% shared custody threshold and 1.5 multiplier—is essential.

The Income Shares Model

Idaho calculates support using both parents' combined "Guidelines Income" (gross income after specific adjustments) to estimate child-rearing costs, then prorates that amount between parents based on their income shares.

• Step 1: Calculate each parent's Guidelines Income
• Step 2: Add to get combined Guidelines Income
• Step 3: Compute each parent's percentage share
• Step 4: Look up Basic Child Support Obligation (BCSO) using progressive schedule
• Step 5: Apply parenting time adjustment if applicable
• Step 6: Add childcare, medical, and other costs proportionally

What Counts as Guidelines Income

Idaho broadly defines Guidelines Income to include:

• Employment income: Wages, salaries, commissions, bonuses
• Self-employment: Gross receipts minus ordinary and necessary expenses (straight-line depreciation)
• Investment income: Dividends, interest, trust income
• Benefits: Pensions, Social Security, workers' compensation, unemployment, disability, veterans' benefits
• In-kind benefits: Company car, housing, meals that reduce personal expenses
• Maintenance received: Alimony from current or prior cases

Overtime exclusion: Overtime may be excluded if all five conditions are met: voluntary, hourly/part-time, no manipulation, parent works full-time 48+ weeks/year, and current income is used. This exclusion doesn't apply to self-employed parents.

Income Adjustments

Reduce gross income by these amounts to get Guidelines Income:

• Court-ordered support/maintenance: From other cases
• Maintenance in present case: Spousal support ordered in this proceeding
• Other children in home: Deduct one-child table amount for natural/adopted children from other relationships living with that parent
• Support paid without order: If proven pattern of payment exists

The Progressive Schedule

Idaho's BCSO schedule is progressive by income brackets:

• First $50,000: Successive $10,000 bands with declining percentages
• Next $100,000: Successive $20,000 bands
• Next $290,000: Single band to reach the cap
• Combined income cap: $440,000/year—above this, courts consider additional factors

You apply each percentage to its income band and sum the results to get the total BCSO, then allocate by income share.

Parenting Time Adjustments

Idaho measures parenting time by annual overnights. The 25% threshold (approximately 92 overnights) is critical:

• Primary custody (≤25% overnights): Standard calculation—obligor pays their income share to the primary parent
• Shared custody (>25% each): Use the 1.5 multiplier method (see below)
• Split custody: Each parent has at least one child primarily—prorate per child with 1.5 for matched children
• Extended visits: 14+ consecutive days may qualify for 50% abatement during that period

Shared Custody: The 1.5 Multiplier

When each parent has more than 25% of annual overnights (92+ nights each), Idaho recognizes the increased cost of maintaining two households:

1. Calculate BCSO: From combined income and number of children
2. Multiply by 1.5: Shared-BCSO = BCSO × 1.5
3. Allocate by income: Each parent's baseline = Shared-BCSO × their income share
4. Weight by other parent's time: Multiply baseline by percentage of time child spends with the other parent
5. Offset: Parent with larger obligation pays the difference

Need a Deeper Analysis?

The calculator above gives you a quick estimate. For a comprehensive analysis covering Idaho's progressive schedule, shared custody multiplier, and add-on costs, get your full Idaho child support analysis here. For official worksheets, use the Forms 6 and 7.

Low-Income Protections

Idaho protects low-income obligors:

• $800/month threshold: If monthly income is below $800, court must review carefully to preserve minimum self-support
• $50 minimum: Rebuttable presumption of at least $50/month per child
• "Rarely zero": Guidelines explicitly caution that support should rarely be set at zero

Add-Ons: Childcare, Medical, Transportation

Beyond basic support, these costs are shared proportionally:

• Work-related childcare: Shared pro-rata by income
• Health insurance premiums: Prorated; employer-sponsored coverage preferred
• Uninsured medical: Shared pro-rata; single treatment over $500 requires advance agreement
• Transportation: Long-distance travel costs may be allocated
• Tax benefits: Dependency exemption assigned to parent with greater benefit; pro-rata share to non-claiming parent
• "Reasonable cost": Medical coverage capped at 5% of obligor's gross income

Duration of Support

Idaho child support continues until:

• Age 18: Standard termination
• High school extension: May continue until graduation or age 19, whichever comes first (court discretion)
• No compelled college support: Courts cannot order post-majority support absent parental agreement
• No disability extension: Idaho has no statute compelling support for disabled adult children

Modification Standards

Idaho uses different thresholds depending on how modification is sought:

• Agency review (Child Support Services): 15% AND $50/month difference required — check if you qualify
• Judicial modification: Substantial and material change in circumstances
• Review cycle: Agency reviews every 3 years, or sooner if sustained change (6+ months)
• Anti-retroactivity: Modifications apply only to installments after filing date

Enforcement and Arrears

Idaho enforces support through Child Support Services:

• Immediate income withholding: Default in all orders unless good cause exception
• Tax refund intercepts: Federal and state refunds, lottery winnings
• License suspension: Driver's, professional, recreational—broad authority under Family Law License Suspension Act
• Passport denial: Federal denial for arrears
• Liens and levies: Against property and accounts
• Contempt: Willful nonpayment may result in jail

Interest on Arrears

Idaho charges judgment interest on delinquent support:

• FY 2026 rate: 9.125% per year (July 2025 - June 2026)
• Interest type: Simple (not compounding), calculated on 365-day year
• Rate calculation: Weekly average 1-year U.S. Treasury yield + 5%, set annually by State Treasurer
• When it starts: From due date of each missed installment

Common Calculation Mistakes

• Using gross instead of Guidelines Income: Must apply adjustments (other children, maintenance) first
• Forgetting 1.5 multiplier: Shared custody (>25% each) requires the multiplier
• Wrong overnight threshold: 25% = approximately 92 overnights triggers shared calculation
• Ignoring progressive schedule: Each income band has different percentages—must sum them correctly
• Assuming age 18 ends support: High school extension may continue to 19
• Missing extended visit abatement: 14+ consecutive days qualifies for 50% reduction

Key Takeaways

• Income Shares model: Both parents' Guidelines Income combined, allocated proportionally
• $440,000 combined cap: Highest cap among states—additional support discretionary above cap
• 25% threshold (92 nights): Triggers shared custody calculation with 1.5 multiplier
• Extended visits: 14+ consecutive days = potential 50% abatement
• $800 low-income threshold: Court must preserve minimum self-support
• $50 minimum per child: Rebuttable presumption
• 15% AND $50 agency threshold: Required difference for agency-initiated modification
• 9.125% arrears interest: Simple interest from due date

For more information about Idaho divorce processes, see our Idaho divorce timeline and filing checklist. For property division information, review our Idaho marital property guide.