What happens to child support if my former partner starts a new family?

Australia’s child support system can be daunting and complex. It becomes more complex when life circumstances change. A common question many parents ask is: What happens if my ex has more children after we separate? Will this reduce the child support I receive, or increase the amount I pay?

This article explains how child support works, what changes when a parent has more children, and what options are available if you believe the assessment is no longer fair.

How child support works in Australia

In Australia, Services Australia (formerly the Department of Human Services) calculate child support using a standard formula. This formula considers both parents’ income, the number of children they have, and the care arrangements in place. 

If one parent has more children later, this can affect the child support assessment.

Services Australia uses a formula that considers:

• each parent’s taxable income;
• the cost of raising children, based on research into average costs;
• the number and ages of children;
• the percentage of care each parent provides (for example, 70/30 or 50/50).

The formula aims to share the costs of raising children fairly, according to each parent’s capacity to pay. You can read more about this in our earlier blog, “How is child support determined in Australia?”

What happens to child support when a parent has more children?

If your ex-partner has more children after you’ve separated, Services Australia will take that into account in future child support assessments. Here’s how:

• Recognising “relevant dependent children”: If your ex-partner has new children living with them, and they are financially responsible for those children, those children are treated as relevant dependent children.
• Adjusting income available for child support: Before calculating child support, Services Australia reduces your ex-partner’s income by a set “exempt amount” to recognise the cost of supporting the additional children.
• Impact on payments: This usually means your ex-partner’s “child support income” is reduced, which may result in you receiving less child support if you are the receiving parent.

It’s important to note that this does not remove their responsibility to support your child. The system is designed to balance obligations fairly across all of a parent’s children.

Example: child support calculation when one separated partner has more children

• • Parent A and Parent B have two children together. Parent A is the paying parent of child support.
  • Parent A later has another child with a new partner.
  • When Services Australia reassesses Parent A’s child support obligations, it recognises the new child as a “relevant dependent child.”
  • Parent A’s assessable income for child support is reduced before calculating the payments for the original two children.

The result: Parent A still pays child support, but the amount may be lower because they are now responsible for supporting three children, not two.

Does this work the same for both parents?

Yes. The rules about new children apply to both parents, not just the one paying child support. 

Services Australia looks at the responsibilities of both parents when working out what is fair.

If the paying parent has more children

When the parent who pays child support goes on to have more children, their income (for the purposes of child support assessment) is reduced by an “exempt amount” before the calculation is made. This reflects the cost of raising those new children. Because the formula sees them as having less income available for child support, the amount they are required to pay for their existing child or children may decrease.

If the receiving parent has more children

The same principle applies if the parent who receives child support has more children in their care. Their income is also reduced by an “exempt amount” to account for the cost of raising those children. 

This adjustment can affect the outcome in two ways:

• • If the receiving parent’s income is treated as lower, the paying parent may need to contribute more because the receiving parent is considered to have less capacity to meet the children’s costs.
  • In other cases, the overall amount of child support can go down. This often happens when both parents’ adjusted incomes are closer together after the calculation, or when the paying parent’s income is lower.

The formula tries to balance responsibilities so that each parent is contributing fairly to all of the children they are legally responsible for. 

Who counts as a relevant dependent child?

The child must be in your care for at least 128 nights a year.

Relevant dependent children include your:

• • biological children;
  • adopted children;
  • step-children if a court order says you have a duty to maintain them;
  • children from artificial conception procedures or surrogacy arrangements. 

Step-children are generally not considered “relevant dependent children” unless a court order or legal obligation requires the parent to support them. 

Challenging a child support assessment

If you believe that your former partner’s new circumstances unfairly affect the amount of child support you receive or pay, you may be able to apply for a “Change of Assessment”. 

Services Australia can review child support assessments where:

• the costs of raising your child are higher than usual (for example, due to medical needs or private schooling);
• the other parent has reduced income but is actually able to earn more;
• there are special circumstances that make the standard formula unfair.

Key things to know about additional children and child support

• Child support is meant to cover all of a parent’s children fairly.
• Having new children does not erase responsibility for existing children.
• Services Australia applies a formula designed to distribute support fairly.
• Parents can request a review if they think the formula produces an unfair outcome.

Practical steps for parents

If you’re concerned about how new children affect your child support payments, here are some practical steps:

Check the current assessment

Log in to your Services Australia account to view the calculation.

Ask for a reassessment if circumstances change

You or your ex-partner can notify Services Australia when new children are born or become dependent.

Keep records of care arrangements and expenses

Evidence of time spent with children or higher costs may help in a Change of Assessment application.

Consider a private agreement

Some parents prefer to set up a Binding Child Support Agreement or Limited Child Support Agreement, which allows more flexibility and certainty than the standard formula.

Seek legal advice

An experienced family law solicitor can help if you believe the child support outcome is unfair or if you are negotiating a private agreement.

GET ADVICE FROM AN EXPERIENCED FAMILY LAWYER:  08 6245 0855

Frequently asked questions

Does my ex-partner having more children mean I won’t get any child support?

No. The obligation to support existing children remains. However, the amount may be reduced depending on your ex-partner’s income and the number of new children.

What if my ex deliberately has more children to lower child support?

The law recognises new children as relevant dependents regardless of intent. However, if you believe your ex-partner is manipulating their income or not meeting their child support obligations, you may apply for a Change of Assessment.

Can private school fees or medical costs be considered in child support assessments?

Yes. These can be grounds for increasing child support through a Change of Assessment if the standard formula doesn’t adequately cover your child’s needs.

Do step-children count when calculating child support?

Generally, step-children are not considered “relevant dependent children” unless a court order or legal obligation requires the parent to support them.

Get help from a family lawyer

Life after separation is not always straightforward, and child support is one area where circumstances can change significantly over time. If your ex-partner has more children, Services Australia will adjust the child support assessment to reflect their new responsibilities. This may lower the payments you receive, but their obligation to support your child does not end.

If you’re worried that a new assessment is unfair, or not properly meeting your child’s needs, you can apply for a review. Every family situation is different, and it’s important to get clear information from a family lawyer about your rights and options.