Income percentage

Income percentage in the Australian child support formula is each parent’s share of the combined child support income. Child support income is each parent’s income minus the self-support amount, and income percentage is calculated by dividing each parent’s amount by the combined total.

Income percentage reflects relative income, not actual spending. It is compared with each parent’s cost percentage (based on care) to determine the final payment outcome.

Definition

Income percentage is worked out by dividing a parent’s child support income by the combined child support income of both parents and expressing the result as a percentage.

Definition source: Guides to Social Policy Law, Child Support Guide, Version 4.97, released 20 March 2026, Income percentage.

What income percentage means

Income percentage is each parent’s share of the combined child support income. To get there, you first subtract the 2026 self-support amount of $31,046 from each parent’s ATI. ATI stands for adjusted taxable income, which for most parents is simply their taxable income.

You then divide each parent’s child support income by the combined total.

A parent with the larger share of the combined child support income has the larger income percentage. This percentage represents each parent’s share of financial responsibility in the child support formula.

How income percentage is calculated

Father near mother pointing toward a Westpac ATM, illustrating financial responsibility and payment decisions in a child support context

Income percentage is calculated by comparing each parent’s child support income to the combined total. Child support income is each parent’s ATI (adjusted taxable income) minus the self-support amount.

Child support income = ATI − self-support amount
Combined income = Parent 1 + Parent 2
Income percentage = (Parent income ÷ Combined income) × 100

Take Ken and Barbie. Ken’s taxable income is $150,000 and Barbie’s taxable income is $100,000. After subtracting the 2026 self-support amount of $31,046, their child support incomes are $118,954 and $68,954. Combined, this equals $187,908.

Ken: $118,954 ÷ $187,908 = 63.3%
Barbie: $68,954 ÷ $187,908 = 36.7%

These percentages show each parent’s share of the combined income. They represent each parent’s share of financial responsibility for the child.

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How income percentage affects formula payments

Income percentage is compared with each parent’s cost percentage, which reflects how much of the child’s costs they meet through care.

Child support percentage = income percentage − cost percentage
  • A positive percentage means the parent pays child support
  • A negative percentage means the parent receives child support

Continuing the example, Ken’s income percentage is 63.3%. If his cost percentage is 24%, his child support percentage is 39.3%.

If the total annual cost of the children is $20,000, Ken pays 39.3% of that amount, which is $7,860 per year.

How income estimates change the result

Income percentage is based on the income used in the assessment. If a parent’s income drops by 15% or more, they can elect to use an income estimate instead of the previous financial year.

That estimated income replaces the earlier income figure in the calculation. This can change the combined child support income and shift each parent’s income percentage. The estimate is later checked against actual income and adjusted if needed.

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