New to Child Support Australia: What Happens and What to Expect

Nothing starts automatically after separation. A child support assessment in Australia begins when a parent applies to Services Australia — and the assessment starts from the date that application is lodged, not the date of separation. Timing matters from day one.

What Happens First After Separation

A child support assessment under the Child Support (Assessment) Act 1989 (CSA Act) is an administrative process — not a court proceeding. Services Australia applies a legislated formula to both parents' financial and care information and issues a formal notice setting out what one parent must pay the other.

For the parent who will receive support, applying sooner almost always means more money overall — because the assessment starts from the date the application is lodged with the Registrar, not the date of separation. For the paying parent, understanding the process early reduces surprises and helps with financial planning.

Step 1: Starting a Child Support Case

Either parent can apply for a child support assessment through Services Australia — online via myGov, by phone on 131 272, or at a service centre. Opening a case does not mean going to court. It is an administrative process where the Registrar applies the child support formula under the CSA Act.

What you'll need to start:

• Your Tax File Number (TFN) and the other parent's TFN if you have it
• Proof of identity
• The children's names and dates of birth
• Your best current estimate of the care arrangement (percentage of nights)

Services Australia will contact the other parent once an application is received. Both parents then have the opportunity to provide their income and care information.

Step 2: Confirming Parentage

Before an assessment can be issued, Services Australia must be satisfied that the person being assessed is a legal parent of the child under the CSA Act. In most cases this is straightforward — both parents are named on the birth certificate and there is no dispute.

Where parentage is disputed or unclear, Services Australia can request a declaration or, in some cases, a parentage test. The assessment will not be issued until parentage is established. If the other parent disputes parentage, seek legal advice early — the process can take time, and any resulting assessment will start from the application date, not the date parentage is confirmed.

Step 3: How the Assessment Is Calculated

Australia uses an administrative formula under the CSA Act — not judicial discretion — to calculate child support. The formula considers:

• Both parents' adjusted taxable incomes (ATI) from the last relevant financial year
• The number of children being assessed
• The ages of the children (older children attract a higher child support income share under the Costs of the Children table)
• The percentage of care — how many nights per year each parent has the children
• Each parent's self-support amount — a fixed deduction from ATI, the same for both parents, updated each 1 January (CS Guide 1.1.S.20)

The formula produces an annual liability. It is recalculated whenever there is a change in income, care, or a new child support period begins.

Step 4: Income and What Services Australia Uses

Adjusted taxable income (ATI) is the income measure used in Australia's child support formula under CSA Act section 5(1) and CS Guide 1.1.A.20. A parent's ATI is the total of:

• Taxable income
• Reportable fringe benefits total
• Target foreign income
• Total net investment losses
• Tax-free pensions or benefits (including certain Centrelink payments)
• Reportable superannuation contributions

Services Australia uses ATI from the last relevant financial year — the most recently processed ATO tax assessment. If a parent's income has reduced by 15% or more from the figure used in the assessment, they can elect to use an estimate of their current income instead (CS Guide 1.1.I.20). The estimate is reconciled with actual income after the financial year ends, and any shortfall becomes a debt.

If no ATO assessment exists for a parent for 2 or more income years prior to the last relevant year, a default income of at least two-thirds annualised MTAWE may be applied (CS Guide 1.1.D.20). This is an important protection against assessments based on missing income data — but it can also produce figures that don't reflect the parent's actual circumstances.

There is also an income cap: the Costs of the Children table used in the formula caps out when the parents' combined child support income exceeds 2.5 times MTAWE (CS Guide, COTC table). Above that threshold, assessed costs do not increase further — meaning very high-income payers do not face an unlimited liability. If you believe the formula produces an unjust result because of a parent's income, property, or financial resources, you can apply for a Change of Assessment in Special Circumstances under the CSA Act.

Step 5: Your Assessment Notice Is Issued

Once parentage and income are confirmed, the Registrar issues an assessment notice (CS Guide 1.1.A.120). Under CSA Act section 76, the notice must show:

• The assessed child support liability as both an annual rate and a daily rate
• The start date of the assessment (the date the application was lodged)
• The income figures and care percentages used in the calculation
• Each parent's right to object if they disagree with the particulars

Read the notice carefully. If the income figures or care percentages are wrong, you have 28 days to lodge an objection with the Registrar under CSRC Act section 80. Objections do not require a lawyer, though complex situations may benefit from legal advice. Acting within 28 days is critical — it is much easier to challenge a fresh assessment than to unwind an entrenched figure later.

Step 6: Choosing How Payments Are Collected

It is the payee who determines which collection method applies (CS Guide 7.3 intro). There are two options:

Private collect

The payer pays the payee directly. Services Australia assesses the amount but does not collect or transfer it. Services Australia cannot enforce payment in a private collect arrangement. This works well when both parents have a functional relationship and payments are consistent. If the payer is applying, private collect is the default unless the payee elects agency collect.

Agency collect

Services Australia collects from the payer and pays the payee. The liability is enforceable — the Registrar has extensive enforcement powers including wage deductions, tax refund interception, and bank garnishment. If the payee is applying, agency collect is the default. The payee can switch to agency collect at any time without the payer's agreement.

Why Dates and Timing Matter

A child support assessment starts from the date the application was lodged with the Registrar (CS Guide 1.3 history). This means:

• Every month of delay is a month of potential entitlement the payee cannot recover
• The assessment does not start from the date of separation or the date the notice is issued
• There is no standard mechanism to backdate beyond the application date

For the receiving parent, applying as soon as the care arrangement is reasonably settled is the right move. For the paying parent, understanding when the liability starts helps you plan finances and avoid accumulating unexpected debt.

Common Mistakes Newly Separated Parents Make

Waiting too long to apply

Every week of delay is a week of potential entitlement that cannot be recovered. If care arrangements are still being negotiated, you can apply on the basis of current arrangements and update later — the assessment will be recalculated when care changes are notified.

Assuming an informal arrangement is enough

Informal agreements have no legal standing and cannot be enforced. Only a formal administrative assessment under the CSA Act, or a child support agreement accepted by the Registrar, carries legal weight if one parent stops paying.

Not checking the income figure used

Services Australia uses ATI from the last relevant financial year. If the other parent's income has grown significantly since their last return, or your own income has dropped by 15% or more, the default figure may not reflect reality. Check the income used in the assessment notice as soon as it arrives.

Missing the 28-day objection window

Under CSRC Act section 80, parties to an assessment can object to the particulars of the administrative assessment. You have 28 days from the date the notice is issued. Missing this window means a far more complex review process through the Administrative Review Tribunal (ART).

Confusing the AAT with the ART

The Administrative Appeals Tribunal (AAT) was replaced by the Administrative Review Tribunal (ART) on 14 October 2024 (CS Guide 1.1.A.40). If you are reading older information that refers to the AAT, that body no longer exists — review applications now go to the ART.

Mixing up private collect with no assessment

Choosing private collect does not mean there is no formal assessment. The assessment remains in place; Services Australia just does not handle the money transfer. But critically — Services Australia cannot enforce payment in a private collect arrangement. If the payer stops paying, the payee must apply to switch to agency collect before enforcement can begin.

Not keeping records

Cash payments and verbal agreements are very difficult to evidence in a dispute. Keep payment records, care diaries, and written communications from day one.

When to Act Early — and What Records to Keep

Act early if: you are the likely payee; you believe the other parent's income is being concealed or understated; your own income has dropped 15% or more since your last tax return; there is any dispute about parentage; or you want a formal arrangement rather than relying on goodwill.

What to Do Next

1. Apply now. The assessment starts from the application date, not the date of separation. Every week of delay is a week of potential entitlement the payee cannot recover.
2. Check the income figures the moment your assessment notice arrives. If they are wrong, you have 28 days to object under CSRC Act section 80. Missing this window makes a correction significantly harder.
3. Know your collection default. Agency collect applies if the payee applied; private collect if the payer applied. The payee can switch to agency collect at any time without the payer's agreement — and Services Australia cannot enforce payment in a private collect arrangement.
4. If your income has dropped 15% or more from the figure used in your assessment, elect an income estimate immediately (CS Guide 1.1.I.20). The estimate is reconciled with your actual income after the financial year ends.
5. Start keeping records today. Care nights, bank transfers, and written communications are the evidence base for any future dispute.