Calculate your child support when you have children from more than one relationship. This calculator uses the official Services Australia multi-case allowance formula to show how supporting multiple families affects your payment.
In Step 1 (Income), click "Other Cases (Formula 3)" to add children from your other child support cases. Enter each child's age — the calculator will automatically apply the Multi-Case Allowance to reduce your child support income and show the impact on your payment.
Your Income
Other Parent's Income
Multi-case child support applies when a paying parent has children from more than one relationship and is assessed to pay child support for children in multiple cases. This is sometimes called "Formula 3" in the Services Australia child support guide.
Without multi-case rules, a parent could be assessed as if each case existed in isolation — potentially resulting in combined obligations that exceed what they can reasonably afford. The Multi-Case Allowance prevents this by recognising the total cost of all children across all cases.
The standard child support formula has 8 steps. In a multi-case situation, an extra calculation is inserted at Step 6 that reduces the paying parent's child support income. Here's how:
Multi-case rules are triggered when a parent has children in at least two separate child support cases. Common scenarios include:
Multi-case does not apply to children who live with you but have no child support case (those are "relevant dependents", which are handled separately in our calculator).
When a parent has multiple cases, special caps apply to the Minimum Annual Rate (MAR) and Fixed Annual Rate (FAR):
Our calculator automatically applies all of these caps and shows the impact in the results breakdown.
Mark earns $95,000 and has 2 children (aged 8 and 10) with his ex-wife, plus 1 child (aged 3) with a second ex-partner. Without multi-case rules, he'd be assessed separately for each case on his full income. With the Multi-Case Allowance, his child support income is reduced by the total cost of all 3 children, resulting in a lower payment for each family.
Sarah earns $70,000 and has primary care of 1 child (aged 12) from her first relationship — she receives child support for this child. She also has 1 child (aged 5) with a different partner where she has only 30% care — she pays child support in this case. The multi-case allowance applies to the case where she pays, reducing her payment to account for the child she primarily cares for in the other case.
Multi-case child support is the formula Services Australia uses when a parent has children from more than one relationship and is paying child support for both. It applies a Multi-Case Allowance that reduces the paying parent's income to recognise they are supporting children across multiple families.
Yes. The Multi-Case Allowance deducts the total cost of all your children (from all cases) from your income before calculating each case. This results in a lower child support income and therefore lower payments per case. The more children you have across cases, the greater the reduction.
Relevant dependents are children who live with you but have no child support case — they reduce your income by a percentage (24% for one, up to 40%+ for three or more). Multi-case allowance applies to children who are in separate child support cases — it reduces your income by the actual cost of those children from the Costs of Children table. If a child has a case, use multi-case. If they don't, use relevant dependents.
Yes. In Step 1 (Income), click "Other Cases (Formula 3)" and add the ages of children from your other child support cases. The calculator will automatically apply the Multi-Case Allowance and show the full breakdown including any MAR/FAR caps.
Multi-case situations are complex. Not sure if you're getting a fair deal?