Alaska Child Support Calculator — How Rule 90.3 Works

The Income-Percentage Foundation

Alaska calculates child support using a percentage-of-income model under Civil Rule 90.3. The formula depends on which custody category applies — and that's determined entirely by overnight counts.

Primary Custody (Under 110 Overnights for Non-Custodial Parent)

When one parent has the child for 256 or more overnights (70%+ of the year), child support is a flat percentage of the non-custodial parent's adjusted annual income:

• 1 child: 20%
• 2 children: 27%
• 3 children: 33%
• Each additional child beyond 3: add 3%

Only the non-custodial parent's income matters here — the custodial parent's earnings don't reduce the base obligation.

Shared Custody (110+ Overnights for Each Parent)

When each parent has the child for at least 110 overnights, both incomes enter the calculation and the math gets more involved:

1. Calculate what each parent would owe under the primary formula, as if the other parent had primary custody
2. Multiply each parent's theoretical obligation by the percentage of time the child spends with the other parent
3. Subtract the smaller figure from the larger — the parent with the higher adjusted figure is the obligor
4. Multiply the difference by 1.5

The 1.5 multiplier reflects the higher combined household costs of maintaining two primary-residence-level homes. If the resulting shared-custody amount exceeds what the obligor would have paid under straight primary-custody math, the obligation is capped at the primary amount.

Adjusted Annual Income: What Counts, What's Deducted

Gross income includes virtually everything: wages, salary, tips, overtime, bonuses, commissions, self-employment income, rental income, unemployment benefits, disability payments (VA and SSDI), non-taxable military allowances (BAH, BAS, COLA), and the annual Permanent Fund Dividend. Need-based public assistance (TANF, SSI) is excluded.

Allowable deductions under Rule 90.3:

• Federal, state, and local income taxes, Social Security, and Medicare
• Mandatory retirement contributions (employer-required pension plans)
• Voluntary retirement contributions (401k, IRA, TSP) — but combined mandatory and voluntary retirement deductions are capped at 7.5% of gross wages
• Health insurance premiums for the parent's own coverage — capped at 10% of total income
• Court-ordered child or spousal support from a prior relationship that's actually being paid
• In-kind support for prior children living in the parent's household (calculated using the Boothby Chart)
• Work-related childcare costs

The High-Income Cap and Low-Income Floor

High income: Standard percentages apply only to the first $138,000 of adjusted annual income. Above that, the court may order additional support only if the other parent demonstrates that a higher amount is justified by the children's specific needs and standard of living.

Low income: Parents earning $30,000 or less calculate their adjusted income using both the standard deduction method and a flat $7,500 standard deduction, then use whichever produces the lower figure.

Minimum support: If the calculated monthly obligation comes out below $50, the court imposes a floor of $50 per month ($600/year) for all children combined, absent a specific variance.

The 110-Overnight Cliff

The gap between 109 and 110 overnights creates a sharp financial discontinuity. A parent with 109 overnights pays a flat percentage of their income with no consideration of the other parent's earnings. At 110, the shared-custody offset formula dramatically changes the math — typically reducing the obligation because both incomes are weighed against each other.

This incentivizes parents to negotiate overnights for financial reasons. Courts are aware of this dynamic and may scrutinize schedules that appear designed to land on a particular side of the threshold rather than genuinely serving the child's developmental needs.

The Alaska Custody & Parenting Plan Guide includes a child support calculation worksheet with worked examples for both primary and shared arrangements, so you can project your obligation before completing Form DR-305.

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