Your assessment isn't permanent
Many parents assume their child support assessment is fixed once it's calculated. It's not. Life changes — incomes go up and down, care arrangements shift, children grow older, new partners and new children come into the picture. The child support system is designed to accommodate these changes.
There are two main ways to change your assessment: an automatic update (when new income information becomes available) and a change of assessment (COA) application when your circumstances don't fit the standard formula.
Use our Child Support Change Calculator to estimate how a change in income or care would affect your payments, and our Child Support Estimator to model different scenarios.
Important: This article is general information only and not legal advice. For advice specific to your situation, contact Services Australia on 131 272 or speak with a family lawyer.
When your assessment automatically changes
Services Australia automatically updates child support assessments when:
- New tax return data is available: Each year, the ATO shares income data with Services Australia. If your taxable income has changed, your assessment adjusts accordingly.
- A child turns 13: The Costs of Children Table has different rates for children under 13 and children 13 and over. When a child crosses this threshold, the assessment recalculates.
- A child leaves the assessment: When a child turns 18 (or finishes secondary school if still attending), they leave the child support assessment.
- Indexed amounts change: The self-support amount, minimum annual rate, and income cap are indexed annually.
Reporting a change in income
You don't have to wait for your tax return to be processed. Either parent can lodge an income estimate with Services Australia if their current-year income is expected to be lower than the income used in the assessment.
This is common when:
- You've lost your job or had hours reduced
- Your business income has dropped
- You've taken parental leave
- You've moved to part-time work
Warning: If your actual income turns out to be higher than your estimate, you may face a reconciliation — meaning you'll owe back-payments. Only estimate lower if you're genuinely confident your income will be lower.
Reporting a change in care
If the number of nights your children spend with each parent has changed, either parent can notify Services Australia. The assessment will be recalculated from the date the change actually occurred.
Even a shift of one night per week can change your care percentage band, potentially changing child support by thousands of dollars per year. Read our care percentage guide for details on how the bands work.
Change of Assessment (COA): the 8 special circumstances
When the standard formula doesn't reflect your real situation, you can apply for a Change of Assessment. Services Australia will consider your application if it falls under one of 8 special circumstances (called 'reasons'):
Reason 1: High costs of caring for, educating, or training the child
If the child has unusually high costs — for example, a disability requiring specialist care, private school fees, or expensive medical treatment — the receiving parent can argue the formula amount doesn't cover the actual costs.
Reason 2: High costs of contact with the child
If the paying parent incurs significant costs to spend time with the child — for example, interstate or long-distance travel for regular visits — this can be used to argue the formula doesn't account for the real cost of maintaining the relationship.
Reason 3: The child support assessment is unfair because of the income, earning capacity, property, or financial resources of either parent
This is the most commonly used reason. Examples include:
- A parent earning below their actual capacity (choosing to work part-time without a valid reason)
- A parent receiving a large inheritance or property settlement
- A parent with significant assets generating income that doesn't appear in their taxable income
Reason 4: The child support assessment is unfair because of the income, earning capacity, property, or financial resources of the child
Applies when the child has independent income or assets — for example, a trust fund, inheritance, or significant employment income.
Reason 5: The child support assessment is unfair because of the duty to maintain another person
If the paying parent supports a new partner or stepchildren who are unable to support themselves (due to disability or age), this can justify a reduction in the assessment.
Reason 6: The child support assessment is unfair because of the direct support given to the child by the paying parent
If the paying parent provides significant direct support — buying school uniforms, paying school fees directly, purchasing medical equipment — that isn't reflected in the formula, they can argue for a credit against the assessed amount.
Reason 7: Necessary commitments to support themselves or another person
If the paying parent has unavoidable financial commitments — for example, debts incurred for the benefit of the family before separation — that reduce their capacity to pay.
Reason 8: A parent's income has been reduced due to the impact of the other parent's income
This is less common but applies when one parent's income has been affected by the other parent's actions — for example, if the receiving parent's career was affected because they supported the paying parent's career during the relationship.
The COA process step by step
- Apply to Services Australia: You can apply online, by phone (131 272), or by lodging form CS1974. Both parents will be notified.
- Gather evidence: You'll need to support your application with documents — payslips, bank statements, receipts, medical reports, or other evidence relevant to your reason.
- The other parent responds: Services Australia gives the other parent an opportunity to respond to your application (usually 28 days).
- A decision-maker reviews the case: A Senior Case Officer at Services Australia reviews the evidence from both parties and makes a decision.
- Decision issued: Both parties are notified of the outcome. The decision may increase, decrease, or leave the assessment unchanged.
Timeframes
A COA application typically takes 6-12 weeks from lodgement to decision, depending on complexity and whether the other parent provides a timely response. During this period, the existing assessment continues to apply.
Appealing a COA decision
If you disagree with the COA decision, you can:
- Object to Services Australia: Lodge an objection within 28 days of receiving the decision. A different officer reviews the case.
- Appeal to the Administrative Appeals Tribunal (AAT): If the objection is unsuccessful, you can appeal to the AAT within 28 days of the objection decision.
- Apply to a court: In limited circumstances, you can apply to the Federal Circuit and Family Court to depart from the assessment.
Tips for a successful application
- Choose the right reason: Match your circumstances to the most relevant of the 8 special circumstances. You can cite multiple reasons.
- Lead with evidence: Assertions without supporting documents are given little weight. Bank statements, payslips, invoices, and medical reports carry more weight than verbal claims.
- Be specific with numbers: Use our Child Support Change Calculator to quantify the impact of the change you're requesting.
- Respond promptly: If you're the responding parent, meet the 28-day deadline. Failure to respond means the decision-maker only hears one side.
Getting help
- Services Australia Child Support: 131 272
- Legal Aid: Free legal advice for eligible parents in every state and territory
- Family Relationship Advice Line: 1800 050 321
- Community legal centres: Many offer free family law advice — find your nearest at clcs.org.au
