Child support in Australia is calculated by Services Australia using a formula that depends on two things you can document: each parent's income, and the percentage of care each parent provides. Most disputes — and most under- or over-assessments — come down to documentation. This guide covers what to keep, why it matters, and how to use it.
Why documentation matters
- Care percentages drive the formula. A 20% care percentage and a 35% care percentage can mean very different annual payments.
- Provisional incomes get used when tax returns aren't lodged. Your evidence may be the only thing pushing Services Australia to revise an artificially low figure.
- A Change of Assessment is a paper exercise. The Registrar reviews documents — your verbal account is not enough.
- Disputes get reviewed years later. The records you didn't keep three years ago are the ones you wish you had.
What to keep — by category
Income documents - Your own ATO Notice of Assessment for every year since separation - Payslips (current and historical) - Bank statements (helpful for showing actual income for self-employed parents) - Business records if self-employed (BAS, P&L) - Centrelink income statements
Care percentage evidence - A nightly log of which parent had the children overnight - Handover times and locations (calendar entries, texts confirming handover) - School pickup/drop-off records - Photos with timestamps from special occasions (births, holidays) - The parenting plan or court orders setting out the schedule
Communication - All texts, emails and app messages about care arrangements, changes, refusals or agreements - Brief notes of phone or in-person conversations made at the time
Expenses you may want included For a Change of Assessment based on high costs: - School fees, uniforms, books, excursions - Medical, dental, optical, allied health (especially for chronic conditions or special needs) - Activities and equipment - Transport costs related to spending time with the children (long distances) - Receipts dated, with the child's name where possible
Evidence of the other parent's circumstances (only if relevant) - Public business records (ASIC, social media, websites suggesting income) - Property records (if alleging undisclosed assets) - Anything obtained legally — never private documents you weren't entitled to access
Care percentage: the most contested number
Services Australia uses care brackets: - 0–13% = nil - 14–34% = regular - 35–47% = shared - 48–52% = equal - 53–65% = primary - 66–86% = above primary - 87–100% = sole
Moving across a bracket boundary changes the assessment significantly. A consistent nightly log is the single most valuable document you can have.
How to use your documents
For a standard assessment Lodge a child support application with Services Australia. You'll be asked for income and care information. The other parent is contacted; their figures are used too.
When care actually changes Notify Services Australia in writing as soon as the pattern changes. Provide your log. Don't wait until the end of the year — back-payments and overpayments are painful.
For a Change of Assessment You apply in writing under one of the 10 reasons listed in the legislation. The Registrar circulates your application to the other parent, gathers responses, and decides on documents. Common reasons supported by documentation: - High costs of the children (medical, education) - A parent's income, property or financial resources don't reflect capacity - High costs of contact with the children
For objections and reviews You can object to a decision within 28 days. The objection officer reviews the file. Beyond that you can apply to the Administrative Review Tribunal — which is, again, document-driven.
Keep it for as long as it could matter
Child support obligations can be reviewed back several years. Family Tax Benefit reconciliations look back to the financial year. Keep documents for at least seven years, and ideally until the youngest child turns 18 plus a few years.
Practical setup
A simple folder structure works: - /income/2024, /income/2025 - /care-log/ (a single rolling file) - /communication/ (export texts periodically) - /expenses/2024, /expenses/2025 - /assessments/ (every Services Australia letter)
Apps like Bloom keep the care log, communication and expenses in one place with timestamps, which is exactly what reviewers want to see.
What not to do
- Don't fabricate or adjust dates — it destroys credibility.
- Don't include speculation in your records ("she was probably hiding income").
- Don't share documents with the children.
- Don't post anything on social media that could contradict your own records.