AustraliaHow is child support calculated in Australia?
Child support in Australia is calculated using a formula set out in the Child Support (Assessment) Act 1989, based on parents’ incomes, care time, and the number and ages of children.
What the Law Says
The calculation of child support in Australia is governed by a statutory formula in the Child Support (Assessment) Act 1989. This formula determines the annual rate of child support payable by the liable parent to the carer.
The formula considers each parent’s adjusted taxable income (based on ATO data), the percentage of care each provides (minimum 35% for shared care to trigger cost-sharing), the number of dependent children, and their ages. It also applies a self-support amount (indexed annually) to ensure the paying parent retains enough income for basic needs.
The Department of Social Services administers the scheme, and Services Australia calculates assessments using the formula. The formula is applied automatically unless parents agree to a binding or limited child support agreement under Part 6 of the Act.
Indexation occurs each year on 1 July, adjusting the self-support amount and other thresholds in line with the Consumer Price Index.
Statutory TextThe formula for working out the annual rate of child support is set out in section 46.
— Child Support (Assessment) Act 1989, s. 46 — Formula for working out annual rate of child support
Statutory TextThe self-support amount is prescribed by the regulations and is indexed annually on 1 July.
— Child Support (Assessment) Act 1989, s. 41 — Self-support amount
Statutory TextA parent has at least 35% care of a child if the child spends at least 128 nights per year with that parent.
— Child Support (Assessment) Act 1989, s. 55C — Meaning of 'percentage of care'
What to Do
Confirm your current care arrangement and calculate the percentage of nights the child spends with you (minimum 128 nights = 35% care).
Provide your most recent tax return or ATO income information to Services Australia.
Use the official Child Support Calculator on humanservices.gov.au to estimate your assessment.
Apply for a formal assessment through Services Australia if no private agreement is in place.
Review your assessment annually — it may change due to income shifts, care changes, or indexation on 1 July.
Sources
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South KoreaNot legal advice. This article is general information based on publicly available sources, written for educational purposes. Laws change and individual situations vary. Consult a licensed attorney in your jurisdiction before acting on anything you read here. Last reviewed: 2026-06-08.