AusChildSupport
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The Australian formula, explained

How child support is calculated in Australia

The formula estimates the cost of raising the children, allocates that cost according to each parent's share of combined child support income, and recognises costs already met directly through care.

General information and estimates only. Only Services Australia can issue a formal assessment.

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The formula in one view

Income sets the share. Care recognises costs already met.

The basic formula compares two percentages for each parent and each child. For formula-specific worked cases beyond this overview, see the Formula 1-6 worked examples.

Income percentage−Cost percentage=Child support percentage
Positive child support percentage×Cost of the child=Estimated annual rate
Income percentage
The parent's share of combined child support income.
Cost percentage
The share of costs treated as being met directly through care.
Child support percentage
The difference between those two shares for each child.

A positive child support percentage generally identifies an amount payable. A negative percentage generally identifies the parent treated as meeting more than their income share of the child's costs directly through care.

On this page

What changes the result

Income, care and family structure do different jobs.

A useful estimate depends on more than two income figures. Each input belongs to a different part of the calculation.

I

Income establishes capacity

Adjusted taxable income is the starting point. The self-support amount is deducted, along with any relevant dependent child amount and applicable multi-case allowance.

  • Adjusted taxable income
  • Self-support deduction
  • Relevant dependent children
  • Children in other child support cases
II

Care recognises direct costs

Care is worked out for each child, then translated into a statutory cost percentage. It does not simply reimburse recorded spending.

  • Nights or percentage of care
  • Different arrangements for different children
  • Non-parent carers
III

Family structure selects the pathway

The number and ages of the children shape the cost table. Other cases, non-parent care and one-parent income circumstances can select a different formula pathway.

  • Number and ages of children
  • Other child support cases
  • Formula 1-6 circumstances

The 8-step formula

Eight steps, in the order they matter.

Services Australia applies the same basic sequence to standard assessments. Other pathways modify or add to this sequence.

  1. Work out each parent's child support income

    Start with each parent's adjusted taxable income, then subtract the self-support amount and any relevant dependent child amount or applicable multi-case allowance.

    Adjusted taxable income - deductions = child support income
    Why this step matters

    This separates total taxable income from the income available to share the children's costs under the formula.

    DSS Formula 1 source

  2. Work out the combined child support income

    Add the two child support incomes. The result is the combined child support income used in the next steps.

    Parent A child support income + Parent B child support income
    Why this step matters

    The formula needs a shared income pool before it can calculate each parent’s share.

    DSS Formula 1 source

  3. Work out each parent's income percentage

    Divide each parent's child support income by the combined child support income and express the result as a percentage.

    Parent's child support income / combined child support income
    Why this step matters

    This percentage represents the share of the children's costs attributed to each parent by income.

    DSS Formula 1 source

  4. Work out each parent's percentage of care

    Work out the percentage of care for each child. Care is child-specific, so siblings can have different percentages.

    Nights of care / 365, then apply the statutory rounding method
    Why this step matters

    Care recognises that some of the children's costs are already being met directly in each household.

    DSS Formula 1 source

  5. Work out each parent's cost percentage

    Map the care percentage to the statutory care-and-cost table. The cost percentage is the share of costs treated as met directly through care.

    Care percentage -> statutory cost percentage
    Why this step matters

    Care time is not converted dollar-for-dollar. The legislation uses bands and defined cost shares.

    DSS Formula 1 source

  6. Work out each parent's child support percentage

    Subtract the cost percentage from the income percentage for each parent and each child.

    Income percentage - cost percentage
    Why this step matters

    A positive result identifies the share not being met directly through care; a negative result identifies the opposite position.

    DSS Formula 1 source

  7. Work out the costs of the children

    Use the Costs of Children table for the assessment year. The amount depends on combined child support income, the number of children and their ages.

    2026 Costs of Children table lookup
    Why this step matters

    The formula uses a statutory cost model rather than the family's itemised household spending.

    DSS Formula 1 source

  8. Calculate the annual rate payable

    Apply the positive child support percentage to the relevant cost of the child. If both parents have positive amounts for different children, the liabilities are offset.

    Positive child support percentage x cost of the child
    Why this step matters

    This converts the percentage imbalance into an annual amount before any other applicable rate rules or adjustments.

    DSS Formula 1 source

Care and cost are not the same

Care is not a dollar-for-dollar calculation.

The percentage of care describes time with a child. The cost percentage is the share of costs the law treats as being met directly through that care. Statutory bands connect the two.

Moving across a band boundary can change the result. Different children can sit in different bands - and 50/50 care can still produce a payment when income shares differ.

Read more about 50/50 care and child support or when a change of assessment may be relevant.

Official care-and-cost table - current at 29 July 2026
Care percentageNights a yearCare levelCost percentage
0-13%0-51Less than regular0%
14-34%52-127Regular24%
35-47%128-175Shared25% + 2% for each care point over 35%
48-52%176-189Shared50%
53-65%190-237Shared51% + 2% for each care point over 53%
66-86%238-313Primary76%
87-100%314-365More than primary100%

Source: Services Australia, Basic child support formula. Page updated 1 January 2026.

Illustrative Formula 1 example

Equal care, different income.

Morgan and Riley have one child aged 10. They share care almost equally and have no relevant dependent children, other child support cases or non-parent carers.

Morgan's adjusted taxable income
$100,000
Riley's adjusted taxable income
$60,000
Care
182 / 183 nights
Assessment year
2026

Illustrative only. The figures use the 2026 annual values and AusChildSupport's production Formula 1 calculation engine; they are not a Services Australia assessment.

StepMorganRiley
01 - Child support income$100,000 - $31,046
$68,954$60,000 - $31,046
$28,954
02 - Combined income$68,954 + $28,954 = $97,908
03 - Income percentage70.43%29.57%
04 - Care percentage182 nights - 49%183 nights - 51%
05 - Cost percentage50%50%
06 - Child support %70.43 - 50 = 20.43%29.57 - 50 = -20.43%
07 - Cost of the child$14,902 + (($97,908 - $93,137) x 12%) = $15,475
08 - Annual rate20.43% x $15,475 = $3,162 a year
Illustrative resultMorgan pays Riley
$3,162a year
$60.81a week, as a simple annual conversion

Beyond the basic pathway

Australian law contains six related formula pathways.

Formula 1 is the foundation. The other pathways adapt it for different family structures rather than replacing it with an unrelated calculation.

01

Basic single case

Only the two parents care for the children and neither parent has another child support case.

02

Non-parent carer

A non-parent carer, such as a grandparent, has qualifying care in a single-case assessment.

03

Multiple child support cases

A parent has children in another case, bringing multi-case allowances, costs and caps into the calculation.

04

Multiple cases and a non-parent carer

The multi-case and non-parent-carer rules need to operate together.

05

One parent's income can be assessed

A bounded non-parent-carer pathway applies where only one parent's income is available for assessment, including some overseas circumstances.

06

A parent has died

A one-parent income pathway applies where a surviving parent may pay support to a non-parent carer.

Inspect the Formula 1-6 evidence

Estimate and assessment

Why an official assessment may differ.

A difference does not necessarily mean the arithmetic was performed differently. Services Australia may be applying different facts, dates, decisions or legal provisions.

Different factual inputs

  • Updated or different income information
  • Disputed or administratively determined care
  • Relevant dependent children or other cases
  • Incomplete or incorrectly entered information
  • Effective dates and partial child support periods

Different legal treatment

  • Fixed or minimum assessment rules
  • Child support agreements
  • Change-of-assessment decisions
  • Court orders or departure orders
  • Overseas or jurisdictional circumstances
Important boundary

Only Services Australia can issue or change a formal administrative assessment. A private estimate cannot determine disputed facts, make administrative decisions or replace professional advice.

Practical questions

Answers without repeating the whole formula.

Does equal care mean no child support?

No. Equal care usually gives each parent a 50% cost percentage, but their income percentages may still differ. The parent with the higher income percentage can therefore have a positive child support percentage.

Which income figure is used?

The starting point is adjusted taxable income, not take-home pay. Services Australia may use tax information, an accepted income estimate or another amount permitted by the law. The formula then applies the self-support deduction and any relevant deductions.

What happens if a parent's income is zero?

Their child support income may be zero, but the final assessment does not automatically follow from that fact alone. Minimum or fixed annual rate rules, income-support circumstances and other provisions may still need to be considered.

How do a child's age and siblings affect the amount?

The Costs of Children table changes with the number of children and whether they are aged 0-12, 13 or older, or in a mixed-age group. Relevant dependent children and children in other child support cases can also change the income available for this case.

What if the children have different care arrangements?

Care and cost percentages are calculated for each child. Different arrangements can produce different child support percentages and, in some cases, amounts flowing in both directions before they are offset.

Can parents agree on a different amount?

Parents may be able to use a limited or binding child support agreement if the legal requirements are met. An agreement can operate differently from a formula assessment. Consider the Services Australia guidance and obtain legal advice where required.

Is an online estimate legally binding?

No. An AusChildSupport estimate is general information based on the details entered. Only Services Australia can issue a formal administrative assessment, and an online estimate is not legal advice.

Why did Services Australia calculate a different amount?

The official assessment may use different income, care, family or effective-date information, or apply an agreement, decision, order or rule outside a basic private estimate. A difference can be about the legal or factual inputs rather than the multiplication itself.

Source and review record

An inspectable basis, not a trust badge.

The Child Support (Assessment) Act 1989 provides the legislative structure. Registered Notice C2025G00638 is the source for the 2026 Costs of Children Table; the DSS Child Support Guide and Services Australia provide operational explanation.

01

Registered Notice C2025G00638

2026 Costs of the Children Table for child support periods starting in 2026, including the $14,902 amount and $93,137 boundary used in this worked example.

Open source
02

DSS Child Support Guide

Formula 1-6 pathways and operational explanation. Guide version 5.00, released 1 July 2026.

Open source
03

Services Australia

Basic eight-step formula and care-and-cost explanation. Its consumer page is corroborative, not the source for the 2026 $14,902 figure.

Open source
04

Child Support (Assessment) Act 1989

Legislative basis for administrative assessment and formula concepts. Latest compilation C71, effective 1 July 2026.

Open source
05

AusChildSupport review record

2026 assessment year - values effective 1 January 2026 - page last reviewed 29 July 2026.

Full methodology

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