The 25% Shared Custody Rule in Idaho Child Support
When a child spends more than 25% of the overnights with each parent, Idaho multiplies the basic obligation by 1.5, splits it by income share, multiplies each parent’s amount by the other parent’s share of time, and has the parent who owes more pay the difference, capped at the standard amount.
When the rule applies
It is recognized that shared custody raises the overall costs of raising a child. If the child spends more than 25% of the overnights in a year with each parent, an adjustment is made (Rule 120(i)(4)). At exactly 25% or less for one parent, the standard calculation applies, so the line is crossed just above 25%, at about 92 overnights a year.
The computation
Multiply the basic child support obligation by 1.5. Multiply that amount by each parent’s percentage of income. Multiply each result by the percentage of time the child spends with the other parent. Offset the two obligations: the parent who owes more pays the difference. In no event does a parent pay more than he or she would have paid had there been no shared custody and the children lived with the other parent.
An example
The same family as in the worked example, but the father has 40% of the overnights and the mother 60%.
| Step | Amount |
|---|---|
| Basic obligation, two children, $96,000 a year combined | $1,512 |
| Multiplied by 1.5 | $2,268 |
| A owes: 62.5% x $2,268 x B’s 60% of the time | $850 |
| B owes: 37.5% x $2,268 x A’s 40% of the time | $340 |
| A pays the difference (before child care and insurance) | $510 |
At 10% of the overnights the father paid $945 a month before add-ons; at 40% the shared custody adjustment gives $510.
Parents with more than 50% paying
Whenever the calculation has a parent with more than 50% of the overnights paying child support, that parent may show that such a payment is inappropriate considering the factors in the rule. A payer with the majority of the time is possible when that parent has much more income.
Extended visits and split custody
In cases where a parent has 25% or less of the overnights, the court may reduce support if that parent has the child for fourteen consecutive days or more; a reasonable reduction is 50% for the duration of the actual physical custody. Split custody, with each parent having at least one child, has its own offset method. The calculator does not include them.
Questions to bring to an attorney
Ask how the court will count overnights, whether your schedule crosses 25% and whether the paying-parent-with-majority exception could apply.
Try your own schedule
Move the overnight slider in the Idaho child support calculator across 25% to see the switch from the standard method to the shared custody adjustment.
Frequently asked questions
What percentage of overnights is shared custody in Idaho?
More than 25% of the overnights in a year with each parent.
What is the 1.5 multiplier in Idaho child support?
In shared custody the basic obligation is multiplied by 1.5 because of the overall increase in child-rearing costs.
Can the Idaho shared custody amount exceed the standard amount?
No. A parent does not pay more than he or she would have paid had the children lived with the other parent.
How are Idaho overnights counted?
By the number of overnights each parent has the child during one calendar year; the rule’s example counts every other weekend as 52 overnights, or 14%.
Can the parent with the majority of overnights pay support in Idaho?
Yes, if the calculation says so, but that parent may show the payment is inappropriate under the rule’s factors.
Official sources
- Idaho Rules of Family Law Procedure, Rule 120: Idaho Child Support Guidelines
- Form 6: Standard Child Support Worksheet
- Form 7: Shared, Split or Mixed Custody Worksheet
A local family law attorney can review your situation — many offer a free consultation.
This is general information, not legal advice. It is based on the cited Idaho statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Idaho attorney.