Child Support in Australia: How It's Calculated and What You're Entitled To

If you have ever tried to work out what child support you will pay or receive, you have probably found two things at once: the formula is genuinely logical once you see how it fits together, and almost nobody explains it in a way that makes sense the first time. Services Australia's calculator will spit out a number, but it will not tell you why that number is what it is, and that gap is usually where the frustration lives.

This guide walks through the actual formula used to calculate Australian child support in plain English, what the current 2026 figures look like, and how an administrative assessment differs from a private agreement.

The basic formula, explained without the jargon

Child support in Australia is worked out using an eight step formula set out in the Child Support (Assessment) Act 1989. It is not arbitrary. It is built on one core idea: both parents are expected to contribute to the cost of raising their children in proportion to their income, adjusted for how much time each parent actually spends caring for them.

In broad terms, the formula does this:

• First, it works out each parent's "child support income." This is each parent's adjusted taxable income minus a self-support amount (an amount every parent is allowed to keep for their own living costs before anything is counted towards child support) and any allowance for other dependants they support.

  
  

• Second, it adds both parents' child support incomes together to get a combined child support income, and works out what percentage of that combined figure each parent contributes.

  
  

• Third, it works out each parent's percentage of care of the children, and converts that into a "cost percentage" using a table set out in the legislation. The idea is that time spent caring for a child is itself a direct contribution to that child's costs, separate from money.

  
  

• Fourth, it subtracts each parent's cost percentage from their income percentage. This gives a "child support percentage" for each parent. Whichever parent ends up with a positive percentage is assessed as the paying parent, because their share of the costs (based on income) is higher than their share of the costs they're already meeting directly through care.

  
  

• Finally, that percentage is applied to a "costs of children" figure, which represents what it actually costs to raise children at that combined income level, based on tables published by Services Australia. The result is the annual rate of child support payable.

It looks more complicated written out than it is in practice. The calculator does the arithmetic. What actually matters for most parents is understanding the two inputs that drive almost every result: income, and care.

Why percentage of care changes everything

Care percentage is usually where assessments surprise people, because it is measured in nights, not vibes. Services Australia counts the actual nights each parent has the children (or, in some cases, an agreed pattern of care) and converts that into a percentage of the year.

The bands work like this. Below 14% care (fewer than 52 nights a year) counts as below regular care and attracts no cost percentage reduction at all. From 14% to 34% care (52 to 127 nights) is "regular care" and reduces the paying parent's cost percentage by 24%. From 35% to 47% is shared care, starting at 25% and increasing by 2% for every percentage point of care above 35%. Equal shared care, from 48% to 52% (176 to 189 nights, roughly half the year) attracts a 50% cost percentage. Above that, the cost percentage keeps climbing until, at 87% care or more, one parent is treated as providing effectively all of the child's day-to-day costs.

This is why a change in the actual care pattern, not just a change in income, can shift an assessment substantially. Parents sometimes assume child support is simply calculated on income and are caught off guard when a change in overnight stays changes the number more than a pay rise would have.

What the numbers actually look like in 2026 - How is child support calculated in Australia

Some of the values used in the formula are updated every year on 1 January, based on average earnings data. For child support periods starting in 2026, the self-support amount (the amount each parent is allowed to keep for their own costs before child support income is calculated) is $31,046. The minimum annual rate of child support, which can apply where a parent's formula liability would otherwise be very low, is $551 for 2026. The fixed annual rate, which can apply in certain below-regular-care situations, is $1,825 per child.

The "costs of children" tables that convert combined income into an actual dollar figure are also updated periodically to reflect indexation, so rather than reproducing a specific dollar table here (which risks going out of date within months), the most reliable way to see what your own situation actually looks like in dollar terms is Services Australia's online child support estimator, using this year's figures. Treat any child support calculator you find elsewhere online, including ones that are not run by Services Australia, as an estimate only.

How to apply for a child support assessment

Either parent, or in some cases a non-parent carer, can apply for an administrative child support assessment through Services Australia, usually via a myGov account linked to Child Support. You will need details of your income (or an estimate, if your circumstances have recently changed), the other parent's details, and information about the current care arrangement for each child.

Once accepted, Services Australia calculates the assessment using the formula above and registers it. From there, payments can be collected privately between parents or through Services Australia's Child Support Collect service, depending on what the parents choose or what the circumstances require.

Child support assessment vs a private agreement

An administrative assessment is not the only option, and for some families it is not the best fit. Parents can instead enter into a child support agreement, and there are two kinds.

A limited child support agreement is based on an amount that is at least what the administrative formula would produce, and either parent can end it after three years or if their circumstances change significantly enough that a fresh assessment would produce a rate at least 15% different. A binding child support agreement, by contrast, can set an amount above or below what the formula would produce, but both parents must first get independent legal advice before signing, and it is generally much harder to end.

Neither type of agreement is registered as being "better" than the other; they suit different situations. A limited agreement gives some flexibility with a safety net tied to the formula. A binding agreement gives certainty and can reflect a genuinely negotiated outcome, but locks both parents in more firmly, which is exactly why independent legal advice is a legal requirement before signing one, not just good practice.

Common reasons the numbers surprise people

A few things trip people up more than any others. Self-employed parents and those with fluctuating income are often assessed on an income estimate rather than a fixed salary, and that estimate can be reconciled against actual tax return figures later, sometimes producing a debt or a credit. Parents who have started a new relationship or have other dependent children may be entitled to a relevant dependant allowance that reduces their child support income, but this needs to be applied for and evidenced, it does not happen automatically. And parents sometimes forget that a change in care percentage, even one that feels informal, such as picking the kids up more often during school holidays, can genuinely change an assessment if it shifts the underlying care pattern.

If your assessment does not reflect your actual financial capacity or your actual care arrangement, in either direction, you are not stuck with it. Both parents can apply for a "change of assessment" in special circumstances (for example, high costs of maintaining contact with a child, a parent's income not reflecting their earning capacity, or the cost of a child's special needs), and either parent can also seek a court order in some circumstances. This is a distinct legal process from the standard formula and is worth getting advice on before you apply, because a change of assessment application can be reviewed from either parent's side, not just the applicant's.

A note on an area still under reform: the Commonwealth Ombudsman has identified a technical anomaly in the current legislation that could, in a small number of cases, make a parent with very little actual care of a child technically eligible to receive child support. The Australian Government has stated it intends to introduce retrospective legislation in 2026 to correct this. It does not change how the standard formula above works for the overwhelming majority of families, but if your situation involves an unusual care split and something about your assessment doesn't seem to reflect the 35% care principle described above, that is worth raising directly with Services Australia or a family lawyer rather than assuming the online explanation covers your case.

Where to go from here

Child support assessments are formula-driven, but the inputs, especially care percentage and income, are not always straightforward to establish, and getting them right matters. This guide explains how the system is meant to work. It does not replace individual advice about your own assessment, and nothing in this article is a substitute for speaking with Services Australia about your specific case or getting legal advice if your situation is contested or complicated.

If you want a structured, plain-English walk-through of the financial side of separation alongside everything else you're navigating, The Divorce Series covers this as part of a broader, self-paced guide to sorting out the legal side of separation. And if you'd rather just get practical updates as they're relevant to you, Join the Brief.