How Child Support Is Calculated in Australia (2026): The 8-Step Formula, Explained

Child support in Australia is worked out by Services Australia (Child Support), the agency that used to be called the Child Support Agency. The rules sit in one piece of Commonwealth law, the Child Support (Assessment) Act 1989, which means the formula is exactly the same whether you live in Victoria, New South Wales, Queensland, South Australia, Western Australia, Tasmania, the ACT or the Northern Territory. Unlike property settlement or parenting disputes, a standard child support assessment is not decided by a judge. It is a mathematical calculation.

This is an important point of difference from the United States and Canada, where child support tables vary by state or province. In Australia there is a single national formula and a single set of national figures that change once a year. The Federal Circuit and Family Court of Australia only becomes involved in child support in limited situations, for example enforcing a debt, dealing with a departure application, or making orders about adult child maintenance.

Any parent who has the care of a child for at least some of the time, and who is not living with the other parent, can apply for an assessment. A non-parent carer (for example a grandparent) can also apply if they care for the child for at least 128 nights a year and are not the partner of either parent. Applying for an assessment is free.

Services Australia uses an 8-step basic formula for the most common situation, which is two parents and the children of one relationship. The steps work through income first, then care, then the cost of the children, and finally who pays whom.

• Step 1: Work out each parent's child support income. This is their adjusted taxable income minus the self-support amount of $31,046 (2026), and minus a deduction for any other dependent children they support.
• Step 2: Add both parents' child support incomes together to get the combined child support income.
• Step 3: Work out each parent's income percentage, which is their share of that combined income.
• Step 4: Work out each parent's percentage of care, based on the number of nights the children spend with them.
• Step 5: Convert each care percentage into a cost percentage using a legislated table (for example, 14% to 34% of nights equals a 24% cost percentage).
• Step 6: Work out each parent's child support percentage by subtracting their cost percentage from their income percentage. Only a parent with a positive result pays; a negative result means that parent receives support.
• Step 7: Work out the total cost of the children using the Costs of Children table, based on the combined income and the children's ages.
• Step 8: Multiply the cost of the children by the paying parent's positive child support percentage. That is the annual amount of child support payable.

The logic is that both parents are responsible for the cost of their children in proportion to their income, but a parent who has the children a lot is already meeting some of those costs directly through care, so they get a credit for it.

The income used is each parent's adjusted taxable income. This is broader than just salary. It includes taxable income, reportable fringe benefits, reportable super contributions, certain tax-free pensions and benefits, target foreign income, and any net financial investment or rental property losses added back in. Services Australia normally uses the most recent tax return, so the assessment can be based on last year's income until a new return is lodged.

Before any sharing happens, each parent has a self-support amount deducted to cover their own basic living costs. For child support periods starting in 2026 this is $31,046. So a parent earning $60,000 has a child support income of about $28,954 once the self-support amount is taken out.

There is also a cap. For 2026, a parent's child support income is capped at $163,446. If you earn more than that, the formula treats you as if you earned exactly the cap, so a parent on $250,000 and a parent on $400,000 are assessed identically on the basic formula. Separately, the combined income that feeds the Costs of Children table is capped at $232,843 for 2026 (2.5 times annualised male average weekly earnings). Both caps are indexed every year, so always check the current figure before relying on it.

Care is one of the biggest levers in the whole calculation. Your care percentage is almost always based on the number of nights the children stay with you over the year, then converted into a cost percentage using a fixed legislated scale. The cost percentage is the share of the children's costs you are treated as already meeting just by having them.

• 0 to 13% of nights (0 to 51 nights a year): 0% cost percentage
• 14 to 34% of nights (52 to 127 nights): 24% cost percentage (called regular care)
• 35 to 47% of nights (128 to 175 nights): 25% to 49% (shared care, rising 2% per percentage point)
• 48 to 52% of nights (176 to 189 nights): 50% (equal care)
• 53 to 65% of nights (190 to 237 nights): 51% to 75% (shared care)
• 66 to 86% of nights (238 to 313 nights): 76% cost percentage (primary care)
• 87 to 100% of nights (314 to 365 nights): 100% cost percentage

This is why two parents with identical incomes can still have a child support amount payable: whoever has the children fewer nights is treated as meeting fewer of their costs directly, so they make up the difference in cash. It also means a change in the care arrangement, even by a handful of nights across a threshold, can change the assessment, so it is worth telling Services Australia promptly when nights change.

The dollar cost of the children is not a flat percentage. It comes from a legislated Costs of Children table that is built on Australian research into what families actually spend raising children, and it is expressed as net costs after Family Tax Benefit. The table depends on three things: the combined child support income, the number of children (counted up to a maximum of three), and the ages of the children, split into two groups, 0 to 12 and 13 and over.

For 2026, the table works in income bands. As an example, for one child aged 0 to 12 the cost is 17 cents in each dollar of combined income up to $46,569, then $7,917 plus 15 cents in the dollar from $46,570 to $93,137, and the marginal rate keeps stepping down as income rises. Children aged 13 and over attract noticeably higher figures (23 cents in the dollar in the first band rather than 17), which reflects that teenagers cost more to raise.

Because the table changes at age 13, an assessment can rise when a child has their 13th birthday, even if nothing else changes. The full table for the current year, including all the bands and the rates for two and three children and mixed-age households, is published by Services Australia and indexed annually, so use the official table rather than memorising any single figure.

Take two parents, Alex and Sam, with one child aged 9. Alex earns $90,000 and Sam earns $60,000. The child lives mainly with Sam, and Alex has the child about 130 nights a year (regular care).

• Step 1, child support income: Alex $90,000 minus $31,046 = $58,954. Sam $60,000 minus $31,046 = $28,954.
• Step 2, combined child support income: $58,954 plus $28,954 = $87,908.
• Step 3, income percentages: Alex about 67.1%, Sam about 32.9%.
• Steps 4 and 5, care and cost percentages: Alex's 130 nights is regular care (14 to 34%), so Alex's cost percentage is 24%. Sam has the rest, a cost percentage of 76%.
• Step 6, child support percentages: Alex 67.1% minus 24% = 43.1% (positive, so Alex pays). Sam 32.9% minus 76% is negative (so Sam receives).
• Step 7, cost of the child: with a combined income of $87,908 and one child aged 0 to 12, the table gives about $14,118 a year.
• Step 8, the assessment: $14,118 times 43.1% is about $6,080 a year, or roughly $117 a week, payable by Alex to Sam.

These numbers are an illustration using the 2026 self-support amount and Costs of Children figures, rounded for clarity. Your own result will depend on your exact incomes, the children's ages and the precise number of nights. For a free, accurate estimate, use the official online estimator on the Services Australia website, which applies the current year's figures automatically.

If the formula produces a very low or nil amount, a minimum annual rate can apply instead so that there is always some contribution. For 2026 the minimum annual rate is $551 per case. It is generally aimed at parents on very low incomes or income-support payments, and it can be reduced to nil in some situations, for example where a parent has at least regular care of the child.

There is also a fixed annual rate, which for 2026 is $1,825 per child per year, capped at three children (so a maximum of $5,475). The fixed rate can apply where a parent has a low taxable income but is not receiving an income-support payment, which is intended to capture parents whose real means are not reflected in their tax return. A parent can ask for the fixed rate not to apply if it would be unfair in their circumstances.

Both the minimum and fixed rates are indexed each year. They are floors and defaults rather than the normal outcome, and most assessments are worked out using the full 8-step formula described above.

The formula is deliberately blunt, so the law provides two main ways to depart from it. The first is a change of assessment (sometimes called a departure) on the grounds of special circumstances. Services Australia can change an assessment if you can prove at least one of 10 listed reasons, with evidence. These include high costs of spending time with a child, a child's special needs, private school or other agreed education costs, a parent's income or earning capacity not being properly reflected, childcare costs above 5% of child support income for a child aged 12 or under, and necessary self-support expenses such as a disability.

The second route is a child support agreement. Parents can make their own arrangement instead of relying on the formula. A limited child support agreement does not need legal advice but only works where the agreed amount is at least equal to the formula figure. A binding child support agreement can set any amount, higher or lower than the formula, but each parent must get independent legal advice before signing, and it is very hard to undo afterwards.

If you and the other parent simply cannot agree and the issue is not just maths, the Federal Circuit and Family Court of Australia can deal with related questions, such as enforcing arrears or, in limited cases, adult child maintenance once a child is over 18. For most families, though, the starting point is the free administrative assessment, and a change of assessment or agreement is the exception rather than the rule.