Child Support Calculator Guide: How Payments Are Calculated

Child support in Australia is calculated using an 8-step administrative formula managed by Services Australia (formerly the Child Support Agency). The formula is designed to divide the cost of raising children between separated parents in proportion to their incomes and care arrangements.

The steps are: Step 1 — determine each parent's child support income (taxable income minus the self-support amount and any relevant dependent costs). Step 2 — calculate the combined child support income. Step 3 — work out each parent's income percentage (their share of the combined income).

Let's break this down. Step 4 — determine each parent's care percentage (based on the number of nights the child spends with each parent). Step 5 — calculate each parent's cost percentage from the care percentage using a legislated table. Step 6 — calculate each parent's child support percentage (income percentage minus cost percentage).

Step 7 — work out the costs of the children using the Costs of Children Table, which varies by combined income and number of children. Step 8 — calculate the child support amount by multiplying the paying parent's child support percentage by the costs of the children.

The parent with the positive child support percentage pays; the parent with the negative percentage receives. This formula applies regardless of whether parents were married, in a de facto relationship, or never lived together.

Each parent's child support income is their adjusted taxable income (ATI) minus the self-support amount. Your ATI includes taxable income, reportable fringe benefits, target foreign income, tax-exempt foreign employment income, net rental property losses, and certain tax-free pensions.

It doesn't include the Age Pension, Disability Support Pension, or Family Tax Benefit. The self-support amount for 2025-26 is $28,463. This is one-third of Male Total Average Weekly Earnings (MTAWE), annualised, and is designed to ensure each parent retains enough income to support themselves before contributing to children's costs.

Quick reality check. Example: Parent A earns $95,000 taxable income. Their child support income is $95,000 - $28,463 = $66,537. Parent B earns $55,000.

Their child support income is $55,000 - $28,463 = $26,537. If a parent earns below the self-support amount, their child support income is $0, and they're assessed as paying the minimum annual rate of child support ($1,739 for one child support case in 2025-26).

If a parent has other dependent children in their household (from a new relationship), a further deduction applies — the relevant dependent child amount ranges from $5,140 to $7,680 per dependent child, reducing the parent's child support income further.

Step 2 is simple: add both parents' child support incomes. Using our example: $66,537 + $26,537 = $93,074 combined.

Step 3 calculates each parent's income percentage: Parent A has 71.5% ($66,537 / $93,074) and Parent B has 28.5% ($26,537 / $93,074). Step 4 determines care percentage based on the number of nights per year each parent has the child. The thresholds are: 0-51 nights = 0% care ('below regular'), 52-127 nights = specific percentage between 1% and 34% ('regular care'), 128-175 nights = 35-47% ('shared care'), 176-225 nights = 48-52% ('equal shared care'), 226-255 nights = 53-65%, and 256-365 nights = 66-100% ('primary care').

Worth knowing: Step 5 converts care percentage to cost percentage using a legislated table. The key conversion points: 0-13% care = 0% cost, 14-34% care = 24% cost, 35-47% care = 25% + 2% for each percentage point above 35% (so 35% = 25%, 47% = 49%), 48-52% care = 50% cost, 53-65% care = 51% + 2% for each point above 53%, and 66%+ care maps proportionally to higher cost percentages. In our example, if Parent A has the child 100 nights/year (27% care = 24% cost) and Parent B has the child 265 nights/year (73% care = 76% cost): Parent A's child support percentage is 71.5% - 24% = 47.5%.

Parent B's is 28.5% - 76% = -47.5%. Parent A pays; Parent B receives.

Step 7 uses the Costs of Children Table to determine how much it costs to raise the child at the parents' combined income level. The table has six income brackets and varies by the number and age of children.

For a combined child support income of $93,074 and one child aged 0-12, the cost of children is approximately $19,300 per year. For one child aged 13+, it's approximately $24,700. For two children (both 0-12), approximately $27,400.

The table tops out at a combined income of approximately $196,000, above which costs are capped. Step 8: multiply the paying parent's child support percentage by the cost of children. Parent A's child support amount: 47.5% x $19,300 = $9,168 per year, or $764 per month, or $352 per fortnight.

Bottom line? This is the amount Parent A would pay to Parent B. If we change the care arrangement to equal shared care (50/50), Parent A's cost percentage becomes 50%, and their child support percentage drops to 71.5% - 50% = 21.5%.

The annual payment drops to 21.5% x $19,300 = $4,150/year ($346/month). Care arrangements have an enormous impact on child support — moving from 27% care to 50% care in this example reduced the payment by 55%.

Example 1 — modest incomes: Parent A earns $65,000, Parent B earns $40,000, one child aged 8, Parent B has 75% care. Parent A's CS income: $65,000 - $28,463 = $36,537.

Parent B's: $40,000 - $28,463 = $11,537. Combined: $48,074. Parent A's income percentage: 76%.

Parent A has 25% care (91 nights) = 24% cost. Child support percentage: 76% - 24% = 52%. Cost of child at $48,074 combined income: approximately $11,200.

So what does this actually mean? Parent A pays: 52% x $11,200 = $5,824/year ($485/month). Example 2 — high income, equal care: Parent A earns $200,000, Parent B earns $80,000.

Two children aged 6 and 10, equal care (50/50). Parent A CS income: $171,537. Parent B: $51,537.

Combined: $223,074 (capped at $196,000 for the table). Income percentages: Parent A 77%, Parent B 23%. Equal care = 50% cost each.

Parent A CS percentage: 77% - 50% = 27%. Cost of two children (0-12) at capped income: approximately $36,800.

Parent A pays: 27% x $36,800 = $9,936/year ($828/month). Example 3 — one parent not working: Parent A earns $110,000, Parent B earns $0 (stay-at-home parent). One child aged 14, Parent B has 85% care.

In plain English: Parent A CS income: $81,537. Parent B: $0. Combined: $81,537.

Parent A income percentage: 100%. Care: 15% = 24% cost.

CS percentage: 100% - 24% = 76%. Cost of child 13+ at $81,537: approximately $22,500. Payment: 76% x $22,500 = $17,100/year ($1,425/month). That catches a lot of people off guard.

Parents can collect child support in two ways. Private collection means the paying parent transfers money directly to the receiving parent — by bank transfer, cash, or any agreed method.

The assessment is registered with Services Australia, but the government doesn't get involved in the actual payment. This works well when parents have an amicable relationship and the paying parent is reliable. The advantage is flexibility — parents can agree to payments in kind (paying school fees directly, buying clothes, covering activities) and these count toward the obligation.

The short version: CSA collection (now called Services Australia collection) means the government collects the payment from the paying parent's wages (similar to tax withholding) or by direct debit, and transfers it to the receiving parent. The government takes a collection fee of approximately 6.6% from the paying parent. CSA collection is appropriate when the paying parent has a history of late or missed payments, when the relationship is acrimonious, or when the receiving parent simply wants certainty.

Under CSA collection, Services Australia has enforcement powers including garnishing wages, intercepting tax refunds, issuing departure prohibition orders (preventing overseas travel), and registering debts against property. Approximately 55% of child support cases use CSA collection.

Parents can switch between private and CSA collection by contacting Services Australia, with changes taking effect in the next collection period.

If you believe your child support assessment is incorrect or unfair, several options exist. First, update your income estimate: if your income has changed significantly from the tax return used in the assessment, you can lodge an income estimate with Services Australia.

This takes effect immediately but will be reconciled against your actual income at tax time — if you underestimated, you will owe arrears plus a penalty. Second, apply for a change of assessment (reason-based review): this allows you to argue that the formula produces an unjust result due to special circumstances. The 10 recognised reasons include: high costs of contact (travel for long-distance parenting), special needs of the child, high costs of child's education, income not reflecting earning capacity (the other parent could work but chooses not to), high child care costs, and others.

Real talk — A Senior Case Officer at Services Australia reviews the application and can adjust the assessment up or down. Third, object to the decision: if you disagree with a change-of-assessment decision, you can lodge an objection within 28 days. An Objections Officer (independent of the original decision-maker) reviews the case.

Fourth, apply to the Administrative Appeals Tribunal (AAT) for an external review. Fifth, parents can make a binding child support agreement (like a contract) or a limited child support agreement that sets payments at a different level than the formula — but these need legal advice and, for binding agreements, each parent must have independent legal counsel.