Child support with shared or 50/50 custody in Idaho

When each parent has the children for more than 25% of the overnights in a year, Idaho uses a shared-custody calculation instead of the standard one I.R.F.L.P. 120(i)(4). Counting overnights out of 365, the line falls between 91 nights (primary) and 92 nights (shared).

The formula

1. Multiply the basic obligation by 1.5, recognizing the cost of two homes.
2. Multiply that by each parent’s share of income.
3. Multiply each parent’s result by the share of time the children spend with the other parent.
4. Offset the two amounts. The parent who owes more pays the difference.

A parent never pays more than they would if all the children lived with the other parent. And when the paying parent has more than 50% of the overnights, they may show the payment is inappropriate under the factors in I.R.F.L.P. 120(i)(7) I.R.F.L.P. 120(i)(4)(B).

Worked example

Parent A earns $60,000 a year and Parent B $40,000, with two children. Parent B has 110 overnights (30%), Parent A the other 255. The basic obligation for $100,000 combined is $1,542 a month.

• Parent A: $1,542 × 1.5 × 60% × (110 ÷ 365) ≈ $418
• Parent B: $1,542 × 1.5 × 40% × (255 ÷ 365) ≈ $646
• Parent B pays the difference: $228 a month, below the $617 Parent B would pay with the children living full-time with Parent A.

The 25% line matters

With the same incomes, the paying parent owes about $925 a month at 91 overnights and about $805 at 92, because crossing 25% switches to the shared calculation. That is why the exact overnight count deserves care, and why the calculator shows how support changes across the whole range in mediation mode.

Equal (50/50) time

With equal time, support usually still flows from the higher earner. With incomes of $72,000 and $48,000 and two children, the parent earning 60% of the combined income pays about $249 a month in base support. Common equal-time schedules such as alternating weeks, 2-2-3 and 5-2-2-5 all come to 182 or 183 overnights.

Split and mixed custody

When each parent has at least one child living primarily with them, support is computed per child, with the 1.5 multiplier applied to an equal number of children in each home I.R.F.L.P. 120(i)(6). For three children with two in one home and one in the other, one child in each home carries the multiplier. Families where some children are shared and others are not use the same per-child worksheet, Form 7.

Extended visits

In primary custody only, the court may reduce support while the paying parent has the children for 14 or more consecutive days; a 50% reduction for that period is described as reasonable I.R.F.L.P. 120(i)(5).

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