How is child support calculated in Australia?

Child support confuses people because it is arithmetic wrapped in emotion. Strip the wrapping and the national scheme - administered by Services Australia under Commonwealth legislation - follows one consistent idea: children should share in both parents’ capacity to pay, measured by income and time¹²³.

The basic formula, step by step

1. Each parent’s income is taken from the most recent tax assessment, then reduced by a self-support amount (indexed annually) and further adjusted for any other dependent children.
2. The remaining figures are added together to find the combined child support income, and each parent’s percentage share calculated.
3. Each parent’s care percentage converts nights of care into a share of the costs.
4. Combining the two produces who pays whom, and roughly how much.

Notice what is absent: the paying parent’s new partner’s income does not enter the calculation, household budgets are not audited line by line, and fault for the separation plays no part. The formula is deliberately mechanical so that outcomes do not depend on who tells the sadder story. What it rewards instead is accuracy - current tax assessments, honest care records and prompt updates when circumstances change - because every figure in the chain compounds through the final number.

The engine behind step three is the cost percentages table: parents are assumed to meet a proportion of children’s costs directly through hands-on care.

Two refinements catch people out. First, care is measured in nights across a twelve-month window, so one extra overnight a fortnight can move a parent between bands - which is why parenting arrangements and child support should never be negotiated blind to each other. Second, where parents disagree about actual care levels, Services Australia decides on evidence such as school records, messages and third-party observations, not on what the parenting plan aspires to. Paper arrangements that nobody follows unravel quickly when money rides on them.

Care percentages drive everything

Care is measured across the year, not week by week:

• Below regular care (under about 14% of nights): 0% of costs recognised.
• Regular care (roughly 14% to 34%): 25%.
• Shared care (35% to 65%): 50%.
• Primary care (65% to 89%): 75%.
• Above shared care (90% or more): 100%.

Two practical effects follow. First, crossing a band boundary changes money materially - going from four nights a fortnight to five can shift the whole calculation. Second, care must be genuine: courts have stripped back arrangements that exist on paper only.

The cost of children rises with income

The formula applies cost-of-children percentages that increase as combined income grows, up to capped amounts that index each year. Costs also vary with the number and ages of children. Because thresholds move annually, always run current numbers through Services Australia’s online estimator rather than relying on a friend’s figure from years past - our child support assessment FAQ covers the mechanics too.

When the formula gets it wrong

Departures from the formula are possible through a change of assessment process, on defined grounds including:

• a parent’s earning capacity deliberately depressed or inflated;
• extraordinary costs such as disability needs or gifted-children programs;
• substantial assets and resources beyond taxable income;
• large unreimbursed education or travel costs between separated households.

Parents can also contract out of the formula entirely with a binding child support agreement, which survives changed circumstances but demands full disclosure and independent advice, or a more flexible limited agreement sitting atop an existing assessment. The choice between them turns on how much certainty each parent needs versus how likely incomes or care are to move - school fees ending, a career break, teenagers spending more nights with the other parent. Agreements drafted for a moment rather than a childhood tend to resurface as disputes precisely when cooperation is lowest, which is why the drafting stage deserves more time than it usually gets.

When payments stop arriving

Unpaid child support is enforceable, not merely regrettable. Services Australia can arrange employer deductions, intercept tax refunds, refer debts for collection and, in persistent cases, pursue court enforcement including over property. Parents receiving nothing should keep the agency informed rather than negotiating privately from weakness; parents struggling to pay should apply for variation or payment arrangements before arrears snowball, since ignoring assessments compounds both the debt and the credibility problem. Private collection arrangements between civil ex-partners work beautifully right up until they do not - the moment they wobble, convert to formal collection.

When obligations end

When obligations end

Liability generally runs until a child turns eighteen, with an important extension: where the child is completing secondary school in that year, the obligation can continue to the end of the school year. Agreements can extend support further - through tertiary study, for instance - but the statutory formula itself does not. Emancipation events such as marriage can end liability earlier. Parents planning around a birthday should confirm exact dates with Services Australia rather than assuming, because the difference between “turns eighteen in October” and “finishes Year 12 in November” changes who owes what across two school terms.

Common surprises

• New partners’ incomes do not count directly, though new dependants reduce your own assessable income.
• Centrelink family tax benefit generally requires taking reasonable maintenance action first.
• Lump sums, company structures and trusts attract scrutiny.
• Moving overseas does not erase obligations - international arrangements exist for those cases.
• The scheme applies to all parents regardless of whether they ever married or lived together, and applies equally to adoptive and (in defined cases) intended parents - there is no “we were never official” exemption.
• Adult children with a disability may attract support beyond the usual age limits in appropriate cases.

Where child support intersects with property settlement or spousal maintenance, the analysis widens considerably - see spousal maintenance explained and our family law practice .

More plain-language guides live in our family law FAQs and family law resources .

Unsure where you stand? Contact Bell & Senior Lawyers for a free initial chat.

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