Services Australia uses an eight-step formula based on both parents' incomes, the cost of raising children at that income level, and the share of nights each parent has the children. It's not a simple "X% of one parent's income" — both parents' incomes count, and care nights significantly reduce or increase liability.

The eight steps

1. Each parent's child support income = adjusted taxable income − self-support amount (~$31,046 in 2026). 2. Combine the two to get combined income. 3. Each parent's income % = their CS income ÷ combined. 4. Each parent's care % = nights of care ÷ 365. 5. Convert care % to cost % using the care/cost table (e.g. 14–34% care = 24% cost). 6. Look up cost of the children from the Cost of Children Table (depends on combined income and number/ages of children). 7. Each parent's child support % = income % − cost %. 8. The negative-result parent pays the absolute value of (their child support % × cost of children) to the positive-result parent.

The Cost of Children Table

A Government table showing how much it "costs" to raise children at different combined parental income levels. For 1 child at combined income up to $46,569: 17% of combined income. Brackets get progressively flatter — over $232,843 combined income, the cost is capped at around $28,407/yr (1 child). The table caps to prevent perverse outcomes at very high incomes. Income bands are set at 0.5×/1×/1.5×/2×/2.5× annualised MTAWE ($93,137 in 2026), matching the official 2026 Costs of Children Table.

Care nights matter a lot

Below 52 nights/yr (1 night/week), no care cost reduction. From 52 to 127 nights, you get a 24% reduction. Equal-shared care (176–189 nights) gives 50% — meaning whoever earns more pays the difference. The dramatic step at 52 nights creates a planning incentive worth noting.

What this calculator doesn't model

Multi-case parents (children with different other parents), additional dependents, non-parent carers, special-needs assessments, and binding child support agreements override the formula. Capacity-to-earn cases (where Services Australia imputes income) need a personal assessment. For any binding figure, use the Services Australia Child Support Estimator or contact them directly. This tool is for rough planning only.