Child Support Calculator Australia: How the Formula Works

This guide walks through Australia's eight-step child support formula using the 2026 figures, with a worked example. Every number here is an estimate only; the binding figure comes from a Services Australia child support assessment, not from this page. Readers who want to run their own numbers can use the Australia child support calculator instead.

This article explains how the Australian child support formula works, using the 2026 figures, for general educational purposes. It is not a calculator, does not collect your financial information, and does not produce a binding assessment. For an actual assessment, apply directly to Services Australia.

Why this page is an explainer, not a calculator

Child support in Australia is legally assessed only by Services Australia, using each parent's actual, verified income and care details. A calculator, including the worked example on this page and our child support estimator, cannot access a parent's real tax return or verify a percentage of care, so any figure it produces is an estimate, not an assessment. This page instead walks through the same eight-step process Services Australia uses, so a reader can understand how the numbers fit together, and points to Services Australia's own tools for a figure that actually counts.

Step 1-3: income, self-support and combined income

The formula starts with each parent's adjusted taxable income, generally their taxable income plus certain additions such as reportable fringe benefits, reportable superannuation contributions and net rental property losses. From each parent's adjusted taxable income, a self-support amount is deducted, reflecting the basic cost of supporting themselves; for the 2026 Child Support Period this amount is $31,046 per parent. What remains after that deduction is each parent's child support income. The two parents' child support incomes are then added together to produce the parents' combined child support income, which is the figure used later to look up the total cost of the children in the Costs of the Children Table. A parent whose income is below the self-support amount contributes nothing to the combined child support income from that source.

Step 4-5: income percentage and care percentage

Each parent's income percentage is their own child support income divided by the combined child support income, expressed as a percentage. Separately, each parent's percentage of care of the child is worked out, generally based on the number of nights, or in some cases a broader pattern of care, the child spends with them each year, then converted into a cost percentage using a standard care-and-cost table that recognises costs do not scale in a straight line with nights of care. A parent's child support percentage is then found by subtracting their cost percentage from their income percentage. A positive child support percentage means that parent pays, but only if the other parent has at least 35 per cent care of the child: under section 40C of the Act, a parent with less than 35 per cent care cannot receive child support under the basic formula, so the amount for that child is nil. A nil or negative result means the parent does not pay, because their share of the children's costs is already being met through their own care.

Step 6-8: the Costs of the Children Table and the final figure

The parents' combined child support income is applied to the Costs of the Children Table, set out in Schedule 1 to the Child Support (Assessment) Act 1989 as percentages of income bands tied to average male earnings and converted into dollar amounts each calendar year, to find the total cost of the children, based on the number of children and their ages. That total cost is then multiplied by the paying parent's child support percentage to produce their annual rate of child support, which Services Australia then converts into a periodic payment amount. Minimum and fixed annual rates can override this result in specific low-income circumstances rather than following the full formula; see child support in Australia for those thresholds. The final figure from an actual Services Australia assessment also accounts for matters this simplified walkthrough does not, such as relevant dependent children, multi-case allowances and income estimates.

A worked example using 2026 figures (illustrative only)

Composite scenario for illustration only, not a real case. Suppose two parents have one child aged 8. Parent A has an adjusted taxable income of $80,000 and Parent B has $50,000. After each deducts the 2026 self-support amount of $31,046, Parent A's child support income is $48,954 and Parent B's is $18,954, for a combined child support income of $67,908. Parent A's income percentage is around 72 per cent and Parent B's around 28 per cent. If Parent B has the child 237 nights a year (65 per cent care) and Parent A has 128 nights (35 per cent care, the lowest level of shared care), their cost percentages are found from the relevant care-and-cost table and subtracted from their income percentages to find each parent's child support percentage. With 35 per cent care, Parent A's cost percentage is 25 per cent, and with 65 per cent care Parent B's is 75 per cent, so Parent A's child support percentage is about 47 per cent (72.09 minus 25). The 2026 Costs of the Children Table for one child aged 0 to 12 at a combined income of $67,908 gives $7,917 plus 15 cents for each dollar over $46,569, or about $11,118, so Parent A's estimated annual liability is about $5,235 (roughly $436 a month). Because Parent B has more than 35 per cent care, the section 40C nil rule does not apply. This example is illustrative only; it is not a substitute for an actual assessment, and small differences in reported income or care nights can change the result.

Getting a binding figure

To get the figure that is actually payable, apply directly to Services Australia for a child support assessment, or manage an existing case through Services Australia's Child Support Online Services via myGov. Services Australia's own published guidance explains how the assessment formula works and what documents are needed. Nothing on this page, including the worked example above, is a substitute for that process, and no figure calculated here should be relied on for negotiating an agreement, budgeting, or a court application.

What can change the outcome from year to year

Because several of the inputs to the formula are not static, an estimate calculated today can become inaccurate well before a full year has passed. A parent's adjusted taxable income changes each time a new tax assessment issues, which can trigger a new child support period. A change in overnight care, even a modest one, moves the care percentage and therefore the cost percentage used in the formula. And the self-support amount, minimum annual rate and fixed annual rate all index on 1 January each year, so an estimate calculated using last year's figures needs to be rechecked against the current Child Support Period rather than assumed to still apply. This is a further reason a one-off calculation, whether from this page or elsewhere, should never be treated as a substitute for an up-to-date Services Australia assessment.

This page provides a general, educational explanation of the Australian child support formula, verified 20 July 2026. It is not a calculator, does not produce a binding assessment, and is not legal advice. For an actual assessment, contact Services Australia; for legal advice, consult a legal practitioner admitted in the relevant Australian state or territory.

For the full legal framework behind these figures, see child support in Australia. For property matters, which are assessed separately, see property settlement in Australia. For the full picture, return to the Australian family law hub.

Frequently Asked Questions

Does this page calculate my exact child support amount?

No. This page explains and works through the formula for educational purposes with an illustrative example. Only an actual Services Australia assessment, based on your real income and verified care arrangements, produces a binding figure.

What is the self-support amount used in the example?

The example uses the 2026 Child Support Period self-support amount of $31,046, which is deducted from each parent’s adjusted taxable income before the remaining incomes are combined.

Why might my actual assessment differ from a rough estimate?

An actual assessment accounts for details a simplified walkthrough does not, such as relevant dependent child amounts, multi-case allowances, income estimates, and the precise care percentage calculated from verified care arrangements, any of which can move the final figure.

How often do the formula figures change?

The self-support amount, minimum annual rate and fixed annual rate index at the start of each calendar year, tied to the Child Support Period, rather than on 1 July like most other Australian legal fees.

What is the Costs of the Children Table?

It is the table, set out in Schedule 1 to the Child Support (Assessment) Act 1989, that sets the dollar cost of raising children at different levels of the parents’ combined income, varying by the number of children and their ages.

Where do I get a real, binding child support figure?

Apply directly to Services Australia for a child support assessment, or manage an existing case through Child Support Online Services via myGov. That is the only source of a figure that is legally binding.

Does percentage of care really change the outcome that much?

Yes. Percentage of care is converted into a cost percentage that is subtracted from a parent’s income percentage to find their child support percentage, so even a modest change in overnight care can shift who pays, and how much, under the formula.