Who can be assessed
To get an assessment you must be the child’s legal parent or a non-parent carer, and at least one parent must live in Australia. A non-parent carer, such as a grandparent, can apply if they care for the child at least 128 nights a year and are not the partner of either parent. The parents must also have agreed to that care. The exception is where it would be unreasonable for the parents to look after the child themselves, such as where the child would be at serious risk of violence or abuse in the relevant parent’s home.
The formula, one step at a time
For parents with only one child support assessment, Services Australia uses a basic formula of eight steps. In short:
Each parent’s child support income
Their adjusted taxable income, less their self-support amount and any dependant allowance that applies.
Combined income
Both parents’ child support incomes added together.
Income percentage
Each parent’s income divided by the combined total.
Percentage of care
How much of the time each parent cares for the child, counted in nights.
Cost percentage
Each parent’s share of the child’s costs met directly through care, read from the care and cost table below.
Child support percentage
Income percentage minus cost percentage. A positive result means that parent pays; a negative result means that parent receives.
Costs of the children
Worked out from the parents’ combined income, the number of children and their ages, using the Costs of Children tables.
The amount
The positive child support percentage multiplied by the costs of the children. If both parents are assessed to pay each other, the amounts are offset.
The cost figures change each year. The current tables, for child support periods starting in 2026, are on Services Australia’s basic formula page.
Care, counted in nights
Care is where the two households meet the formula. The more nights a child spends with a parent, the more of the child’s costs that parent is treated as meeting directly.
| Care level | Care percentage | Nights a year | Nights a fortnight | Cost percentage |
|---|---|---|---|---|
| Less than regular care | 0–13% | 0–51 | 0–1 | 0% |
| Regular care | 14–34% | 52–127 | 2–4 | 24% |
| Shared care | 35–47% | 128–175 | 5–6 | 25%, plus 2% for each percentage point of care above 35% |
| Shared care | 48–52% | 176–189 | 7 | 50% |
| Shared care | 53–65% | 190–237 | 8–9 | 51%, plus 2% for each percentage point of care above 53% |
| Primary care | 66–86% | 238–313 | 10–12 | 76% |
| More than primary care | 87–100% | 314–365 | 13–14 | 100% |
Parents may be able to agree how much care each provides; if they cannot, Services Australia works it out. The evidence it may ask for includes a diary or calendar showing when the children are in your care, records from school or day care, health visits, travel bookings, and a court order or parenting plan together with proof that you are following it. It does not accept statements from anyone under 18. What a court order can say is in parenting orders, and what goes in a written agreement is in parenting plans.
Care levels matter for family payments too: a paying parent who provides below regular care cannot get Family Tax Benefit, for example, and in shared care both parents may be able to share it.
Which income is used
The assessment uses income for the financial year that ended before the current child support period. Before anything else, a self-support amount is set aside from each parent’s adjusted taxable income for their own living costs. As at October 2026 that amount is $31,046 for 2026, and it changes on 1 January each year. Services Australia’s own example: a parent earning $40,000 has a child support income of $8,954; a parent earning $30,000 has a child support income of zero, though minimum payment rules may still apply.
Lodging tax returns on time matters. If a return is late, Services Australia works out a provisional income, and if your real income turns out lower it usually cannot go back and change your child support. Separately, it says it is reviewing assessments based on provisional income from 2008 onwards, and that you do not need to contact it about this unless you have received a letter.
When circumstances change
| Change | What to know |
|---|---|
| Care changes | Tell Services Australia straight away. If it is not told within 28 days, the new level of care may apply only from the date you tell it, you may get a debt or overpayment, or the assessment may be suspended or ended. |
| Care stops following a written arrangement | If a court order, parenting plan or written agreement is not being followed and the parent with reduced care is taking reasonable action, care in the written arrangement may be used for an interim period of between 4 and 52 weeks. |
| Income falls | If your current adjusted taxable income is at least 15% lower than the figure used, you may be able to give an estimate. Only you can make it, and it can be used only from the day you tell Services Australia. |
| Extra income after separating | You can ask for it to be excluded, for example from a second job, with the Application for Post Separation Income to be Excluded form. |
| Getting back together | The assessment can be suspended for up to 6 months; if you are still together after 6 months the case ends. |
| A child turning 18 while at school | Child support normally stops at 18. To extend it to the end of the school year, apply while the child is 17 and still in full-time secondary school. |
Changing an assessment in special circumstances
Services Australia can change an assessment when special circumstances apply, as long as the change would be fair to the child and to both parents. You need evidence of at least one of its 10 reasons, and it says being unhappy with your child support is not a valid reason. It suggests calling its Child Support enquiry line before applying.
The reasons, in brief:
- High costs of spending time or communicating with the child.
- Costs from the child’s special needs.
- Costs of caring for, educating or training the child in the way both parents intended.
- The child’s own income, earning capacity, property or financial resources.
- Money, goods or property already paid or transferred for the child’s benefit.
- Child care costs for a child under 12.
- A parent’s necessary expenses significantly reducing their capacity to support the child.
- One or both parents’ income, earning capacity, property or financial resources.
- A parent’s duty to support another child or person.
- A parent’s responsibility to support a resident child who is not legally theirs.
What the other parent sees. The other parent gets Part B of your application and every supporting document, though not your personal details from Part A. It is up to you to remove details you do not want shared, such as your address, workplace or the children’s school. If either parent appeals to the Administrative Review Tribunal, the whole form goes to the other parent.
What can be withheld. The Tribunal allows Services Australia to withhold your contact details and information that might reveal where you live. For anything else to be withheld, Services Australia must ask the Tribunal for a non-disclosure order, and it will do that on your behalf if it identifies a risk to your health or safety, or someone else’s. You can also ask the Tribunal for one yourself, and the Tribunal decides. If you are worried that sharing personal information could put you or anyone else at risk, Services Australia asks you to let it know.
Objecting to a decision
Read the letter, then call
Services Australia asks you to read the decision letter and call its Child Support general enquiry line if something is unclear or seems wrong. You may object if you think it used wrong or old information, missed facts or did not apply the law correctly.
Object within the time limit
You have 28 days from the day you get the letter (90 days if you live in a reciprocating jurisdiction overseas). Care percentage decisions can be objected to at any time, but changes may not be backdated if the objection arrives after 28 days. Late objections can be asked for, with reasons.
The other parent responds
By law, what you send is shared with the other parent, who can respond. Payments stay the same while the objection is considered, unless a court makes a stay order.
The decision
Services Australia decides within 60 days if both parents live in Australia, or 120 days if one lives in a reciprocating jurisdiction overseas, and explains its reasons in writing.
Review by the Tribunal
If you disagree, you can apply to the Administrative Review Tribunal, generally within 28 days of the objection decision letter. There is no fee for a first review. An appeal to a court after that is only on questions of law.
Some decisions cannot be objected to, including who is a child’s parent, which only a court can decide, and most decisions about collecting payments.
Services Australia’s Child Support enquiry line is 131 272, Monday to Friday 8:30 am to 4:45 pm, and it will arrange an interpreter for free.
If dealing with the other parent is not safe
Services Australia says that if you are worried about risks to you or your family, or something such as financial abuse or family violence makes it hard to tell it about changes, you can call the Child Support enquiry line. You can also call the number you usually use and ask to speak with a social worker, who can connect you with legal help, family violence services and housing support; it says what you tell them stays private unless you agree otherwise.
If you think sharing your personal information could put anyone’s health or safety at risk, Services Australia asks you to let it know.
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