Same numbers. Different result. Here’s why.
In this worked comparison, identical inputs are run through the Services Australia online estimator and this calculator. The estimator path returns $1,696/year payable by Parent 1. This calculator returns $129.31/year payable by Parent 2. The gap is $1,825 — exactly one Fixed Annual Rate. This page explains the difference step by step.
One important distinction
The scenario
Two parents, two children, both under 13. The parents are separated. Parent 1 has the higher income.
Child 1 is a shared care arrangement — both parents exceed the 35% threshold. Child 2 is different: Parent 1 has primary care (72%) and Parent 2 has regular care (28%). That 28% figure is the key. It sits below the 35% shared care threshold.
The results side by side
| Services Australia Estimator | This Calculator | |
|---|---|---|
| Child 1 liability | Parent 1 pays $1,696 / year | Parent 1 owes $1,696 / year |
| Child 2 liability | Not assessed for either parent | Parent 2 owes $1,825 / year (FAR) |
| Offset applied (s.67A)? | No | Yes |
| Final annual result | Parent 1 pays $1,696 / year | Parent 2 pays $129.31 / year |
What actually happened
The Services Australia estimator did not simply ignore Child 2. If you look at the raw formula numbers, $1,696 + $1,628 does not equal $1,696 — meaning the estimator correctly zeroed out Child 2 on Parent 1’s side. It processed enough of the case to know Parent 1 owes nothing for Child 2. It then stopped.
The step it skipped: assessing what Parent 2owes for Child 2, and then offsetting both parents’ liabilities against each other.
Why Parent 2 owes the Fixed Annual Rate
Section 65A of the Child Support (Assessment) Act 1989 sets out the three conditions that trigger the Fixed Annual Rate:
- The parent did not receive an income support payment in the last relevant year of income.
- That parent’s adjusted taxable income is less than the Parenting Payment (single) maximum basic amount — currently $26,720/year.
- That parent has less than 35% care of the child.
Parent 2 meets all three conditions for Child 2. Their ATI is $25,000 — below the $26,720 threshold. They have 28% care of Child 2 — below the 35% shared care threshold. And they do not receive income support. The Fixed Annual Rate of $1,825/year therefore applies to Child 2.
This worked example is checked against the published 2026 fixed annual rate and Parenting Payment (single) threshold. Those values can change by assessment year, so the point is the structure of the case — a mixed standard-formula and fixed-rate offset — not that these dollar figures apply forever.
Key point
- The FAR is not triggered by a “negative child support percentage.” It is triggered by three specific legislative conditions under s.65A — income, care percentage, and income support status.
- This case involves one child running on the standard formula and a second child triggering the FAR for the other parent. In this worked example, that combination is outside the path the Services Australia online estimator completes.
The offset under section 67A
Once both liabilities are established, section 67A of the Act applies the offset. Parent 1 owes $1,696 for Child 1. Parent 2 owes $1,825 for Child 2. The lower amount is set off against the higher:
The direction of payment reverses entirely. Instead of Parent 1 paying Parent 2 nearly $1,700/year, Parent 2 pays Parent 1 $129.31/year. The Services Australia online estimator, by not completing the FAR assessment for Child 2 in this worked example, does not reach this step.
Why the estimator falls short here
The Services Australia online estimator is aimed at simpler Formula 1-style cases where both parents have income and neither child triggers a special rate. It is a public self-service tool, not the same system Services Australia uses to issue formal assessments.
Cases where one child runs on the formula and a second child triggers the FAR for the other parent require the estimator to calculate liabilities in both directions and then apply the s.67A offset. In this worked scenario, the public estimator does not complete that path. The result is an incomplete picture — not a calculation error in the formal assessment system, but a coverage gap in the public estimator.
Frequently asked questions
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