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Australia Child Support Calculator

Estimate child support using Australia's 8-step CSA formula — both parents' incomes, care percentage adjustments, self-support deductions, and change of assessment grounds.

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A$
A$
Annual Child Support Assessment
A$887/month
Annual SupportA$10,646/yr
Total Child CostsA$20,637/yr
Parent A Income Share77%
PayerParent A
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Advanced Calculator

8-step formula walkthrough with step-by-step visualisation, and care percentage impact table showing how nights per year affect the monthly assessment.

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Assessment Inputs
A$
A$
CSA 8-Step Formula Walkthrough
1
Self-Support Amounts
A: A$27,304/yr | B: A$27,304/yr
2
Costs of Children
A$20,637/yr
3
Adjusted Incomes
A: A$67,696 | B: A$20,696
4
Income Shares
A: 76.6% | B: 23.4%
5
Care % (A)
35% → Expense factor: 25%
6
Care % (B)
65% → Expense factor: 76%
7
Net Child Support Payable
A$10,646/yr
8
Monthly Amount
A$887/month
Payer: Parent A pays A$887/month (A$10,646/year)
Professional Simulator

Full CSA income assessment with all income sources, change of assessment grounds (reasons 1–10), and minimum/fixed assessment comparison.

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Parent A — Full Income Details
A$
A$
A$
CSA Income: A$95,000/yr (taxable + fringe benefits + negative gearing add-back)
Parent B & Children
A$
CSA Formula Assessment
A$887/month
PayerParent A
Annual AssessmentA$10,646/yr
Total Child CostsA$20,637/yr
Parent A Income Share76.6%
Parent A Care Expense Factor25%
CSA Income (Parent A)A$95,000/yr

How Australia's Child Support Formula Works

Australia uses an 8-step administrative formula under the Child Support (Assessment) Act 1989, administered by Services Australia. Unlike many countries, Australia's system takes into account both parents' incomes and the actual percentage of care each parent provides.

The formula produces a "basic assessment" — a legally binding annual amount. Either parent can apply for a "change of assessment" if they believe the formula produces an unjust result due to special circumstances.

The 8-Step Formula

Step 1: Calculate each parent's adjusted taxable income Step 2: Subtract the self-support amount (~A$27,304) from each Step 3: Determine costs of the children from the cost table (based on combined adjusted income × number of children) Step 4: Calculate each parent's income percentage Step 5: Determine each parent's care percentage (nights ÷ 365) Step 6: Convert care percentage to cost percentage (below 14% = no offset; above 86% = full cost) Step 7: Determine each parent's child support percentage (income share minus cost percentage) Step 8: Apply to cost of children → annual assessment

Care Percentage Table

Nights/year Care % Cost % 0–51 0–13% 0% 52–127 14–34% 24% 128–175 35–47% 25–48% (scales) 176–189 48–51% 48% 190–237 52–64% 50–76% (scales) 238–312 65–85% 76% 313–365 86–100% 100%

The care percentage is calculated as the number of nights per year the child spends with that parent divided by 365. The cost percentage represents the share of child costs each parent is considered to bear directly through day-to-day care.

Example Calculation

Example: 2 children, standard care arrangements

Parent A taxable incomeA$95,000
Parent B taxable incomeA$48,000
Parent A self-support deductedA$27,304
Parent B self-support deductedA$27,304
Adjusted income AA$67,696
Adjusted income BA$20,696
Parent A care (35% = 128 nights)35% care
Estimated annual assessment~A$7,800/yr

Always verify using the official Services Australia online child support estimator or Child Support Calculator at servicesaustralia.gov.au.

Frequently Asked Questions

The self-support amount is a deduction from each parent's income before the formula is applied — it represents the income each parent needs to support themselves. For 2024–25, the self-support amount is approximately A$27,304 per year (it is updated annually by Services Australia). It is based on a percentage of the Male Total Average Weekly Earnings figure. Even low-income parents retain this protected amount before child support is calculated.
Services Australia uses the parent's "adjusted taxable income" from their tax assessment. This includes taxable income, total net investment losses, reportable fringe benefits, reportable employer super contributions, and certain tax-free government pensions or payments. The formula uses the most recent tax assessment, but Services Australia may also estimate income based on the current year if there has been a significant change, or if a parent has earning capacity greater than their actual income.
Care percentage is the proportion of nights per year a child spends with each parent. One parent having the child for 128 nights equals 35% care. Services Australia uses the term "regular care" for 14–34% (52–127 nights), "shared care" for 35–65% (128–237 nights), and "majority time" for 66–86% (238–312 nights). The care percentage affects both the child support formula (via the cost percentage) and eligibility for certain government payments.
Yes. There are two types: a "limited" child support agreement (no legal advice required, but must be at least the administrative assessment amount) and a "binding" child support agreement (both parents must have independent legal advice). Binding agreements can set amounts above or below the administrative assessment and can also cover non-periodic costs. Either type must be registered with Services Australia to be enforceable.
A change of assessment allows a parent to ask Services Australia to depart from the formula if it would be unjust or inequitable. There are 10 grounds under the Child Support (Assessment) Act including: special financial needs of the child, high necessary expenses, earning capacity not reflected in income, legal duty to support other people, costs of maintaining contact, and property or financial resources. A Registrar considers the application and can increase or decrease the assessment.

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