Looking for a child support calculator in Australia? Services Australia (Child Support) has the official estimator on its website — and it's the only one that matters for your actual assessment. This guide explains exactly how that calculator works, so you understand the numbers it gives you and can roughly estimate your own.
Where the official calculator lives
The only authoritative calculator is the Child Support Estimator on the Services Australia website. Other "child support calculators" online are unofficial — they can be useful for ballpark figures, but the formal assessment is always done by Services Australia.
Direct link: search "Child Support Estimator Services Australia" — the page is on servicesaustralia.gov.au.
How child support is calculated — the 8-step formula
Australian child support uses an 8-step administrative formula. Here's the plain-English version:
Step 1 — Each parent's child support income
Start with each parent's adjusted taxable income (most recent tax return), then subtract a self-support amount (the amount Services Australia says a parent needs to support themselves).
Step 2 — Combined child support income
Add both parents' child support incomes together.
Step 3 — Each parent's income percentage
Work out what percentage of the combined income each parent earns.
Step 4 — Care percentage
How many nights (or hours) of care each parent provides, as a percentage of the year. Standard care brackets:
- 0–13%: nil care
- 14–34%: regular care
- 35–47%: shared care
- 48–52%: equal shared care
- 53–65%: primary care
- 66–86%: above primary care
- 87–100%: sole care
Step 5 — Cost percentage
Each care bracket has a corresponding cost percentage — the share of the children's costs Services Australia considers that parent to already meet through direct care.
Step 6 — Child support percentage
Subtract each parent's cost percentage from their income percentage. A positive number means that parent owes child support; a negative number means they receive it.
Step 7 — Costs of the children
Services Australia publishes a Costs of the Children table each year, based on the parents' combined income and the number and age of the children. This gives an annual dollar figure for what it costs to raise the kids.
Step 8 — Annual rate
Multiply the paying parent's child support percentage by the Costs of the Children figure. The result is the annual child support amount.
A worked example
This is a rough illustration only — always use the official estimator for real numbers.
- Parent A: child support income $60,000
- Parent B: child support income $40,000
- Combined: $100,000
- Parent A's income %: 60%, Parent B's: 40%
- Care: Parent A has 30% care (regular care), Parent B has 70% (primary care)
- Cost percentages (from the table): Parent A 24%, Parent B 76%
- Parent A's child support %: 60% − 24% = 36% (owes)
- Parent B's child support %: 40% − 76% = −36% (receives)
- Costs of the Children for 2 kids on $100k combined income: roughly $20,000/year (illustrative)
- Parent A pays: 36% × $20,000 = $7,200/year, or about $600/month
What counts as income?
- Salary and wages (gross)
- Self-employment / business income
- Investment income (interest, dividends, rent)
- Distributions from trusts
- Some Centrelink payments (most family payments are excluded; payments like JobSeeker count)
- Foreign income
The figure used is your adjusted taxable income from your most recent ATO assessment.
What if a parent isn't lodging tax returns?
Services Australia can use a Provisional Income — often based on previous returns, employer data, or a default amount. If you believe the other parent's income is being underreported, you can apply for a Change of Assessment.
Change of Assessment
A Change of Assessment lets you ask Services Australia to depart from the standard formula. Common reasons:
- One parent's income doesn't reflect their financial capacity
- Special needs of a child
- High costs for the children (private school, medical)
- The paying parent has high costs related to spending time with the children
It's a written application with evidence — get free legal advice before lodging one if you can.
How to get an estimate today
1. Go to the Services Australia Child Support Estimator. 2. Enter both parents' incomes (or estimates). 3. Enter the number and ages of the children. 4. Enter care percentages. 5. The tool returns an annual and weekly estimate.
The result is an estimate — your actual assessment may differ. Only Services Australia can issue a formal Child Support Assessment.
How Bloom helps
Care percentages are the lever most people get wrong, because they're trying to remember a year of changeovers from memory. Bloom lets you log custody nights as they happen, so when it's time to update Services Australia (or query an assessment), you have a real record instead of a guess.
For the formal calculation, always use the Services Australia estimator — Bloom is not a child support calculator and doesn't issue assessments.