AusChildSupport

Australian child support formula

How child support is calculated

Child support in Australia is worked out with a formula set by law. It combines both parents’ incomes with the care each parent provides, and turns them into one yearly amount. This guide explains each step in plain English, with a worked example.

Figures
2026 values
Based on
DSS Child Support Guide
Reviewed
The formula in two linesWorked example, 2026

Income percentage, in the example: 76.16%

−Cost percentage, in the example: 24%

=Child support percentage, in the example: 52.16%

Child support percentage, in the example: 52.16%

×Costs of the children, in the example: $14,118

=Annual rate, in the example: $7,364

Income percentage is the share of the child’s costs a parent is responsible for meeting, based on income. Cost percentage is the share they already meet through care. The costs of the children come from a table set by law, and the annual rate is what’s paid each year. Figures are Parent 1’s, from the worked example.

01The idea

Income sets the share. Care counts as paying part of it.

Raising a child costs money. The formula shares that cost between the parents in line with their incomes. The DSS Child Support Guide calls this an “income shares” approach.

Care counts too. A parent who has the child overnight is already meeting some of the child’s costs directly. So the formula treats care as paying part of that parent’s share.

Child support covers the difference. If a parent’s share of income is bigger than the share of costs they meet through care, they pay the gap to the other parent.

Source DSS Child Support Guide: Formula 1 – the basic formula (2.2.2)

Share of costs by income (income percentage)

Parent 1: 76.16%Parent 2: 23.84%

Share of costs met through care (cost percentage)

Parent 1: 24%Parent 2: 76%
52.16% gap: Parent 1’s child support percentage
From the worked example below, using 2026 values. Each bar adds up to 100%. Parent 1’s share of income is bigger than their share of care, and the difference becomes child support.

02Formula 1

Formula 1, step by step

Formula 1 is the basic formula. It’s used when only the parents care for the child and neither parent has another child support case.

It has eight steps: three for income, three for care, and two that turn the result into dollars. The same example runs through every step.

Source DSS Child Support Guide: Formula 1 – the basic formula (2.2.2); The steps involved in making a child support assessment (2.2.1)

The worked example

A fictional case. Every figure below was calculated by the AusChildSupport estimate engine.

Assessment year
2026
Formula
Formula 1
Parent 1
Adjusted taxable income $98,000 · 104 nights a year
Parent 2
Adjusted taxable income $52,000 · 261 nights a year
Child
One child, aged 10

Steps 1–3Income

  1. Step 1: Work out each parent’s child support income

    Start with each parent’s adjusted taxable income (ATI). ATI is taxable income plus some other amounts, such as reportable fringe benefits.

    Take away the self-support amount. This is a set amount each parent keeps for their own living costs. It’s the same for both parents: $31,046 for 2026.

    A parent who supports other children may take away more: a relevant dependent child amount or a multi-case allowance. What’s left is the parent’s child support income.

    FormulaChild support income = ATI − self-support amount − any amounts for other children

    In the example

    Parent 1$98,000 − $31,046 = $66,954Parent 2$52,000 − $31,046 = $20,954

    Source DSS Child Support Guide: Child support income (1.1.C.120); Adjusted taxable income (ATI) (1.1.A.20); Self-support amount (1.1.S.20)

  2. Step 2: Add the two incomes together

    Add the two child support incomes. The total is the parents’ combined child support income. It’s used again in step 7.

    FormulaCombined child support income = Parent 1’s child support income + Parent 2’s child support income

    In the example

    $66,954 + $20,954 = $87,908

    Source DSS Child Support Guide: Combined child support income (1.1.C.190)

  3. Step 3: Work out each parent’s income percentage

    Divide each parent’s child support income by the combined child support income. The answer is their income percentage: the share of the child’s costs they’re responsible for meeting, based on income. It’s rounded to two decimal places.

    FormulaIncome percentage = child support income ÷ combined child support income × 100

    In the example

    Parent 1$66,954 ÷ $87,908 × 100 = 76.16%Parent 2$20,954 ÷ $87,908 × 100 = 23.84%

    Source DSS Child Support Guide: Income percentage (1.1.I.30)

Steps 4–6Care

  1. Step 4: Work out each parent’s care percentage

    Count the nights the child is likely to spend with each parent over the care period, which is usually 12 months. Turn that into a percentage, then round it to a whole number. The rounding rule is unusual, so it has its own section below. This is worked out for each child, so children in the same case can have different percentages.

    FormulaCare percentage = nights with the parent ÷ nights in the care period × 100, then rounded

    In the example

    Parent 1104 ÷ 365 × 100 = 28.49%, rounded down to 28%Parent 2261 ÷ 365 × 100 = 71.51%, rounded up to 72%

    Source DSS Child Support Guide: Percentage of care (1.1.P.70); Basics of care (4.1.1)

  2. Step 5: Turn care into a cost percentage

    Look up each parent’s rounded care percentage in the cost percentage table. The result is their cost percentage: the share of the child’s costs they’re treated as meeting through care.

    FormulaRounded care percentage → cost percentage table → Cost percentage

    In the example

    Parent 128% care → 24% costParent 272% care → 76% cost

    Source DSS Child Support Guide: Cost percentage (1.1.C.200)

  3. Step 6: Work out each parent’s child support percentage

    Take the cost percentage (step 5) away from the income percentage (step 3). The answer is the parent’s child support percentage. A positive figure means the parent’s share of income is bigger than the share of costs they meet through care.

    FormulaChild support percentage = income percentage − cost percentage

    In the example

    Parent 176.16% − 24% = 52.16%Parent 223.84% − 76% = −52.16%

    Source DSS Child Support Guide: Child support percentage (1.1.C.140)

    A negative child support percentage means a nil rate

    Parent 2’s percentage is −52.16%, so Parent 2 pays nothing for this child. A negative percentage doesn’t automatically mean a parent receives child support. Money only changes hands when the other parent has a positive percentage. To receive child support, a parent must have at least 35% care of the child. See a case where nothing is payable, and the rates that can replace the formula answer.

    Source DSS Child Support Guide: Child support percentage (1.1.C.140); Eligible carer (1.1.E.10)

Steps 7–8Costs and rate

  1. Step 7: Work out the costs of the children

    Use the Costs of Children Table to find the costs of the children: a yearly amount for what the children cost, based on the parents’ combined child support income.

    The table depends on the combined income, how many children there are, and their ages (0–12, or 13 and over). Its figures are updated each year. Amounts are rounded to the nearest dollar at each step.

    FormulaCosts of the children = base amount for the income band + (combined income − start of band) × band percentage

    In the example

    One child aged 10. A combined income of $87,908 falls in the band over $46,569 and up to $93,137.$7,917 + ($87,908 − $46,569) × 15% = $14,118Open this lookup on the Costs of Children Table

    Source DSS Child Support Guide: Costs of the child (1.1.C.210); About the Costs of the Children Table (2.3.1.10); Updating the table, rates and values (2.3.6)

  2. Step 8: Work out the annual rate

    Multiply each positive child support percentage by the costs of the children. The answer is that parent’s annual rate: what they pay each year for the child.

    If both parents have a rate, for example because each cares for a different child, the rates are offset and only the difference is paid. Some cases have further checks before the rate is final, such as the minimum annual rate or the fixed annual rate.

    FormulaAnnual rate = child support percentage × costs of the children

    In the example

    Parent 152.16% × $14,118 = $7,363.95, rounded to $7,364Parent 2negative percentage → nil

    Source DSS Child Support Guide: Formula 1 – the basic formula (2.2.2); Minimum annual rate (2.3.4); Fixed annual rate (2.3.5)

Worked example result · 2026 values

$7,364 a year

Parent 1 pays Parent 2: $613.67 a month, or $141.62 a week. Parent 2’s rate is nil.

03Care

How nights of care become a cost percentage

Care is worked out for each child. It’s usually based on the number of nights the child is likely to spend with each parent over the care period.

Sometimes hours are a better measure. For example, a parent might care for the child every weekday but not overnight.

Source DSS Child Support Guide: Basics of care (4.1.1); Care other than in nights (4.1.4)

  1. Nights104 nights
  2. Care percentage104 ÷ 365 × 100 = 28.49%
  3. Rounded28.49% → 28%
  4. Cost percentage28% → 24%
Parent 1 in the worked example, from nights to a cost percentage.

Rounding: down below 50%, up from 50%

Care percentages are rounded to a whole number, but not in the usual way. Below 50%, the percentage is rounded down. At 50% or above, it’s rounded up.

The cost percentage is then looked up from the rounded figure, never the unrounded one. That means a single night can move a parent into a different band.

One night either side of a band edge
Nights a yearCare percentage, then roundedCare bandCost percentage
5113.97% → 13%Below regular care0%
5214.25% → 14%Regular care24%
12734.79% → 34%Regular care24%
12835.07% → 35%Shared care25%

51 nights or 52. At 51 nights, care rounds down to 13%: below regular care and a 0% cost percentage. One more night gives 14%: regular care and 24%.

127 nights or 128. At 127 nights, care rounds down to 34%: regular care and a 24% cost percentage. One more night gives 35%: shared care and 25%.

An even split. This is where the direction of the rounding shows. A year split evenly is 182 and 183 nights, which is 49.86% and 50.14%. The first rounds down and the second rounds up, so the parents are recorded at 49% and 51%, not 50% each. Both still get a 50% cost percentage.

Source DSS Child Support Guide: Frequently asked questions – care (1.4.3.20)

The cost percentage table

Each rounded care percentage maps to a cost percentage. The table has flat steps and two sliding scales, so small changes in care matter most near a step.

Cost percentage for each rounded care percentageCost percentage is 0% for 0–13% care; 24% for 14–34% care; rising from 25% to 49% across 35–47% care; 50% for 48–52% care; rising from 51% to 75% across 53–65% care; 76% for 66–86% care; 100% for 87–100% care.
The cost percentage rises in steps as care increases. The two dots are the worked example’s parents. The table below lists every value.
Cost percentage table
Care bandNights a yearRounded care percentageCost percentage
Below regular care0–510–13%0%
Regular care52–12714–34%24%
Shared care128–17535–47%25% plus 2% for each percentage point over 35% (25% to 49%)
Shared care176–18948–52%50%
Shared care190–23753–65%51% plus 2% for each percentage point over 53% (51% to 75%)
Primary care238–31366–86%76%
Above primary care314–36587–100%100%
  • A parent with less than 14% care is treated as meeting none of the child’s costs through care.
  • A parent with more than 65% care isn’t assessed to pay child support for that child.

Source DSS Child Support Guide: Cost percentage (1.1.C.200); Below regular care (1.1.B.20); Shared care (1.1.S.40); Primary care (1.1.P.100)

04Final checks

When the formula’s answer isn’t the amount payable

The eight steps produce a rate for each child. A few rules sit on top of that rate, and they can change what is actually paid — in both directions.

A positive percentage doesn’t always mean a payment

To receive child support, a parent must be an eligible carer: someone with at least 35% care of the child. Shared care, primary care and above primary care all clear that line. If the other parent’s care is below it, a positive child support percentage can still produce nothing payable.

A second case, with the same 2026 figures

The child lives mainly with Parent 1, who also earns more.

Assessment year
2026
Parent 1
Adjusted taxable income $120,000 · 256 nights a year
Parent 2
Adjusted taxable income $45,000 · 109 nights a year
Child
One child, aged 10

Steps 4 to 6

Parent 171% care → 76% cost, 86.44% − 76% = 10.44%Parent 229% care → 24% cost, 13.56% − 24% = −10.44%

Nothing is payable for this child. Parent 1’s child support percentage is positive, at 10.44%, but Parent 2 has 29% care — less than the 35% needed to receive child support. Read the other way, Parent 1 has more than 65% care, and a parent with more than 65% care isn’t assessed to pay for that child.

Source DSS Child Support Guide: Eligible carer (1.1.E.10); Shared care (1.1.S.40); Child support percentage (1.1.C.140); Primary care (1.1.P.100)

When each parent has a rate, the rates are offset

Steps 4 to 6 are worked out for each child. When one child lives mainly with each parent, both parents can end up with a rate to pay. The two rates are offset, and only the difference changes hands.

A third case: one child with each parent

Same incomes as the worked example: $98,000 and $52,000, so the income percentages are 76.16% and 23.84%. The costs of the children are $20,685 for 2 children, and the cost of each child is $10,343.

A rate for each child
ChildCareChild support percentageRate payable
Child 1aged 1091%9%−23.84%23.84%Parent 2 pays $2,466
Child 2aged 89%91%76.16%−76.16%Parent 1 pays $7,877

The two rates are offset, so Parent 1 pays Parent 2 the difference: $5,411 a year.

Source DSS Child Support Guide: Formula 1 – the basic formula (2.2.2)

Minimum and fixed annual rates

Two set rates can replace the rate the formula produces. They are the reason a parent whose formula rate is small or nil can still have an amount to pay.

The minimum annual rate is $551 for 2026. It can apply when the rate worked out by the formula is less than that, the parent has below regular care — under 14% — of every child in the assessment, and the fixed annual rate doesn’t apply. A parent’s total is capped at three times the minimum annual rate across their cases, and a parent whose income is less than that total can apply to have it reduced to nil.

The fixed annual rate is $1,825 per child for 2026, for up to three children. It can apply when a parent received no income support payment in the last relevant year of income, their adjusted taxable income for that year was below the maximum basic rate of parenting payment (single) — $26,720 — and they have less than 35% care of the child. A parent can apply for it not to apply.

The fixed annual rate is worked out for each child, so it can also apply to a parent the formula assesses as receiving child support. In a case with more than one child, a parent can be assessed to pay the fixed annual rate for a child in the other parent’s care while being entitled to receive child support for a child in their own. The two amounts are offset, and only the difference is paid.

Source DSS Child Support Guide: Minimum annual rate (2.3.4); Fixed annual rate (2.3.5)

05Formulas 2–6

When a different formula applies

Formula 1 covers the most common situation. There are five other formulas. Each one is a variation of the basic formula for a different family situation.

Source DSS Child Support Guide: The formulas (2.2)

Work through all six formulas with fictional cases

The worked-examples page shows a full breakdown for each formula and three comparisons with examples from the DSS Child Support Guide.

06Your estimate

What an estimate can and can’t tell you

An estimate is

  • An indicative amount, based on the information you enter.
  • Worked out with the formula steps on this page, using the figures for the year you choose.
  • Useful for planning, comparing care arrangements, or preparing for a conversation.

An estimate is not

  • A Services Australia child support assessment. Only Services Australia makes administrative assessments.
  • Legal advice about your situation.
  • The whole picture. Agreements, court orders, changes of assessment and other rules can change what’s payable.

The result is an estimate. It isn’t a formal Services Australia assessment, and it isn’t legal advice. Read how an estimate differs from an assessment, or find out when to talk to a lawyer.

Run the formula with your own figures

The calculator works through these steps with your incomes, care and children, then shows you each step of the result.

Calculate your estimate

07Sources

Sources

This guide follows the DSS Child Support Guide. Where they differ, the Child Support (Assessment) Act 1989 and the registered yearly notices take priority.

Figures for 2026

DSS Child Support Guide sections cited

Reviewed .