Idaho sets child support under Rule 120 of the Idaho Rules of Family Law Procedure, amended effective July 1, 2025, using a marginal-bracket schedule that runs all the way to $440,000 of annual income. Parents who each have more than 25% of the parenting time qualify for shared-custody treatment with a 1.5× multiplier, and Idaho also has a distinct split-custody calculation for when each parent has primary custody of at least one child. This calculator reproduces the rule’s own worked examples exactly.
Key facts
| Model | Marginal-bracket schedule — Idaho R. Fam. L. P. Rule 120 (amended eff. 2025-07-01) |
|---|---|
| Schedule ceiling | $440,000/year |
| Shared-custody threshold | Each parent >25% parenting time (×1.5) |
| Verification | Reproduces the rule’s own worked examples exactly |
Official source: https://isc.idaho.gov/irflp120
Custody arrangements covered
- Standard custody
- Shared custody (each parent >25% parenting time) — 1.5× multiplier
- Split custody — each parent has primary custody of at least one child
Frequently asked questions
What rule governs Idaho child support?
Rule 120 of the Idaho Rules of Family Law Procedure, amended effective July 1, 2025.
How high does Idaho’s schedule go?
The marginal-bracket schedule runs to $440,000 in annual income.
What triggers shared-custody treatment in Idaho?
Each parent having more than 25% of the parenting time, which applies a 1.5× multiplier to the calculation.
Does Idaho have a separate rule for split custody?
Yes — when each parent has primary custody of at least one child, a distinct split-custody calculation applies.
Update history
- — Idaho went live under Rule 120 of the Idaho Rules of Family Law Procedure, with the full marginal-bracket schedule to $440,000/year, shared custody (over 25% each, at 1.5×), and split custody. Reproduces the rule's own worked examples exactly.