Our calculator implements the official Services Australia 8-step child support formula as defined in the Child Support (Assessment) Act 1989 (Cth). This page provides technical documentation for legal professionals and family law practitioners.
Formula Implementation
We implement all six Services Australia formulas with complete accuracy:
Formula 1
Standard Assessment
Two parents, standard separation scenario
Formula 2
Non-Parent Carer
Care provided by grandparent or other non-parent
Formula 3
Multi-Case Assessment
Parent has children in multiple child support cases
Formula 4
NPC + Multi-Case
Non-parent carer with multi-case scenarios
Formula 5
Overseas Parent
Parent in non-reciprocating jurisdiction
Formula 6
Deceased Parent
One parent deceased, non-parent carer applies
The 8-Step Formula
Our calculator follows the official Services Australia methodology:
1
Child Support Income (CSI)
Calculate each parent’s available income: ATI - SSA - Relevant Dependents
2
Combined CSI (CCSI)
Sum both parents’ child support income
3
Income Percentages
Calculate each parent’s share of combined income
4
Care Percentages
Convert nights of care to percentages (with proper rounding)
5
Cost Percentages
Map care percentages to cost percentages using official table
6
Child Support Percentage
Calculate net obligation: Income % - Cost %
7
Cost of Children
Use official COTC tables based on combined income and child ages
8
Final Payment
Multiply child support % by cost of children
Accuracy & Validation
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Official Rates
All rates (SSA, MAR, COTC tables) match Services Australia 2026 values
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Validated Results
Calculator results tested against official Services Australia examples
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Edge Cases
Handles zero payment, high income, low income, and multi-case scenarios
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Annual Updates
Rates updated within 48 hours of Services Australia announcements
2026 Rates & Thresholds
Self-Support Amount (SSA)$31,046/year
Minimum Annual Rate (MAR)$551/year
Fixed Annual Rate (FAR)$1,825/year
MTAWE Cap$232,843/year
Maximum PPS$26,720/year
Note: Relevant dependent deductions are calculated dynamically using the cost of children formula based on the parent’s income, not fixed amounts.
Last updated: February 2026. Rates are reviewed annually.
Limitations & Disclaimers
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Not Legal Advice
This calculator provides estimates only. It does not replace professional legal or financial advice.
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Official Assessment Required
Only Services Australia can make official child support assessments. Our results may differ from official assessments.
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Complex Cases
Change of Assessment applications, court orders, and binding agreements may override calculator results.
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Income Verification
Calculator relies on user-provided income data. Services Australia may use different income figures based on tax returns and other evidence.
For Legal Professionals
This calculator is designed as a preliminary assessment tool for family law practitioners and their clients. We recommend professional consultation for:
Change of Assessment applications (Reason 1-8 factors)
Binding Child Support Agreements
Limited Child Support Agreements
Complex income scenarios (trusts, companies, hidden income)
Court proceedings and consent orders
International child support matters
Departure from assessment applications
Updates & Maintenance
Annual Rate Updates
SSA, MAR, FAR, and COTC tables updated within 48 hours of Services Australia announcements
Formula Changes
Legislative changes implemented within 30 days of enactment
Quarterly Reviews
Comprehensive validation against Services Australia examples
Changelog Available
All formula and rate changes documented with effective dates
Questions About Our Methodology?
For technical questions, partnership inquiries, or to report calculation discrepancies, please contact us.