Idaho Shared Custody Child Support: The 92-Overnight Threshold Explained

Why 92 Overnights Matters

Under IRFLP Rule 120, Idaho's child support formula changes fundamentally at the 92-overnight mark. If the non-custodial parent has 91 or fewer overnights per year (25% or less of the child's time), the standard calculation applies. At 92 overnights, the shared-custody formula kicks in — and the monthly payment can drop by hundreds of dollars.

This is not a gradual curve. It is a hard cutoff that creates significant financial consequences for both parents, and it is one of the most contested aspects of parenting-schedule negotiations in Idaho.

The Standard Formula (91 or Fewer Overnights)

When one parent has the child for more than 75% of overnights, the standard calculation is straightforward:

1. Calculate each parent's monthly Guidelines Income — gross income minus deductions for other court-ordered support obligations and maintenance.
2. Combine both incomes and look up the Basic Child Support Obligation (BCSO) on the progressive schedule. The schedule applies declining percentages across income brackets up to a combined annual cap of $440,000.
3. Calculate each parent's income share percentage.
4. The paying parent's support = BCSO × their income share percentage.

For two parents earning $6,000 and $4,000 per month with one child, the BCSO is approximately $1,000. The higher-earning parent pays 60% of that — $600 per month.

The Shared-Custody Formula (92+ Overnights Each)

When each parent has at least 92 overnights, the calculation recognizes the increased costs of maintaining two full-time households:

1. Calculate the standard BCSO from combined income (same as above).
2. Multiply by 1.5 to get the Shared BCSO: $1,000 × 1.5 = $1,500.
3. Allocate by income share. Parent A (60%): $900 baseline. Parent B (40%): $600 baseline.
4. Weight by the other parent's overnight percentage. With equal time (182.5 nights each = 50%): Parent A's net share = $900 × 50% = $450. Parent B's net share = $600 × 50% = $300.
5. Offset. The parent with the larger net share pays the difference: $450 − $300 = $150 per month.

Compare that to $600 under the standard formula. Same incomes, same child — the only difference is crossing the 92-night line.

The Cliff Effect

This abrupt shift creates a dynamic where adding one overnight — going from 91 to 92 — can reduce support by 50% or more. Both parents and courts are aware of this, and it introduces predictable tension into schedule negotiations.

A parent who pushes for exactly 92 overnights without a genuine caregiving plan risks undermining their position. Judges evaluating the best-interests factors under Idaho Code § 32-717 can usually tell when overnight requests are financially motivated rather than child-focused.

Conversely, a parent who tries to limit the other parent to 91 overnights to keep the standard formula in play faces the same scrutiny. Courts look at the child's needs, not the financial incentives.

Add-On Expenses

Beyond the base BCSO, three categories of child-related costs are allocated proportionally by income share:

• Work-related childcare (daycare, after-school programs)
• The child's portion of health insurance premiums
• Uninsured extraordinary healthcare expenses

Any single non-emergency medical treatment exceeding $500 requires advance notice to and consent from the other parent — or a court order — to be enforceable as a shared expense.

Low-Income Protections

Rule 120 protects low-income obligors through two mechanisms:

• The $800 monthly threshold. If the paying parent's Guidelines Income falls below $800 per month, the court must perform an individualized review of basic living expenses to ensure the parent can maintain minimum subsistence.
• The $50 minimum. There is a rebuttable presumption that every parent should pay at least $50 per month per child, regardless of income. Support is rarely set at zero.

Interest on Arrears

Every missed child support payment immediately becomes a final, enforceable money judgment. Simple interest (non-compounding) accrues from the due date of each missed installment. The annual rate is set by the Idaho State Treasurer — currently 8.875% for fiscal year 2027.

Calculating Accurately

The biggest source of errors in Idaho child support calculations is incomplete income documentation. Self-employment income, bonuses, commissions, rental income, and stock-based compensation all count as Guidelines Income — and the standard calculators miss them if the supporting documents are not thorough.

The Idaho Child Custody & Parenting Plan Guide includes a child support preparation worksheet that walks you through documenting your income, tracking overnights, and running the calculation under both the standard and shared-custody formulas.

See more Idaho guides →