Child Support Calculator Australia

How the 8-Step Formula Works

Services Australia's Registrar follows 8 steps to assess child support where the parents are the only carers and neither has another child support case, known as a single case assessment (Child Support (Assessment) Act 1989 (Cth) s 35). Steps 1 to 3 work out each parent's child support income and combine them into an income percentage. Steps 4 to 6 work out each parent's percentage of care, the matching cost percentage from the Care and Cost table, and a child support percentage (income percentage minus cost percentage). Steps 7 and 8 apply the Costs of the Children table to the combined income, then multiply by the positive child support percentage to get the annual rate payable, offsetting between the parents where both would otherwise owe an amount (s 67A). A parent cannot receive child support for a child of whom they themselves have under 35% care: the annual rate payable to them for that child is nil (s 40C), whatever the formula would otherwise produce.

A parent's child support income is their adjusted taxable income (ATI), less the self-support amount, less any relevant dependent child amount, less any multi-case allowance (CSA Act Part 5 Division 3). For child support periods starting between 1 January 2026 and 31 December 2026, the self-support amount is $31,046 (one third of annualised MTAWE, s 45). If the formula amount for a case works out below $551 a year and the paying parent has less than regular care of every child in the case, the minimum annual rate can apply instead, including where the formula amount is nil (s 66). A separate fixed annual rate of $1,825 per child (capped at 3 children) can apply instead of the minimum rate where that parent's ATI is below the Parenting Payment (single) maximum basic amount ($26,720 for 2026), they did not receive an income support payment in the relevant year, and they do not have at least shared care; where the fixed rate can apply, the minimum rate does not (s 65A, s 66(2)).

The Costs of the Children table (Schedule 1 to the CSA Act) then apportions a dollar cost between the parents from the combined child support income, the number of children, and their ages, capped once combined income passes 2.5 times MTAWE. With more than 3 children the costs are worked out as for 3 children, using the oldest 3 children's ages, then divided by the actual number of children (s 55G(4)). Every dollar amount in the COTC calculation is rounded to the nearest whole dollar at each step (s 156).

Worked Example

This is a recordinglaw-computed worked example using the published 2026 figures, not an official Services Australia example. It uses the same calculation engine as the tool above: a parent with an ATI of $85,000 ("Parent A") who has regular care of two children under 13 (52 nights a year), and a parent with an ATI of $45,000 ("Parent B") who has primary care of those children (313 nights a year).

That works out to about $743 a month, or about $343 a fortnight. Change any of the numbers in the calculator above to see how the result moves for your own situation.

What This Estimate Does Not Cover

The basic 8-step formula this calculator implements is only one part of a real child support assessment. It does not cover a multi-case allowance, which reduces a parent's child support income where they have more than one active child support case and caps what they pay across all of them, a mechanism Services Australia has not published in full. It does not cover a non-parent carer assessment, such as a grandparent or other relative who has care of a child instead of a parent.

The calculator does apply the minimum annual rate ($551 per case) automatically where the formula amount is low or nil and a parent has less than regular care of every child (s 66), and it flags where the fixed annual rate ($1,825 per child) may apply instead, based on your answer to the income support question. What it cannot do is confirm a parent's actual income support history, or whether Services Australia would grant an application not to apply the fixed rate (s 65B) or not to apply an income support presumption (s 66A); those need an actual assessment. It does not model a change of assessment, where either parent applies to have special circumstances taken into account outside the formula, and it does not model an income estimate, which a parent can lodge where their current ATI is at least 15% lower than the income used in their assessment. Finally, it treats each child's age as fixed for the whole year; a real assessment recalculates the Costs of the Children table separately for the periods before and after a child turns 13 during a child support period (s 55G(4)).

Only Services Australia assesses child support. For a fuller estimate, including situations this tool cannot model, use Services Australia's own Child Support Estimator, which shares some of the same limits: its own About page states it cannot estimate a multi-case assessment, a non-parent carer assessment, or compare old and new estimates. See also Child Support in Australia for the full legal explainer.

This tool applies the published Child Support (Assessment) Act 1989 (Cth) basic formula (s 35), current as at 26 September 2026, for the child support period running 1 January 2026 to 31 December 2026. It applies the minimum rate and flags where the fixed rate may apply, but cannot confirm income support status or a s 65B/66A application. It does not model a multi-case assessment, a non-parent carer assessment, a change of assessment, an income estimate, or a child's age changing during the period. It does not access any Services Australia record, does not lodge or change anything, and is not legal or financial advice. RecordingLaw.com is not a law firm and is not affiliated with Services Australia or the Australian Government. Consult a legal practitioner or contact Services Australia for an actual assessment.