How Is Child Support Calculated?

Child support in Australia is determined by a national formula set out in the Child Support (Assessment) Act 1989.

The goal is simple : both parents contribute fairly to their children's needs.

The assessment weighs income, each parent's share of care, and the official costs of raising children to produce outcomes that are consistent and predictable.

Because the scheme is federal, the same rules apply wherever you live, so the calculation works the same in Sydney, Melbourne, Brisbane and Perth.

A parent needs to make an application with Services Australia to determine whether child support is required to be paid by a parent, and if so only then is a parent required to meet these weekly assessed amounts.

Services Australia are unlikely to require a parent to be liable for back pay of child suppprt.
i.e.
if parents separate on 1 January 2024, but an application for child support is only made on 1 January 2025, the parent who is require to pay child support to the other parent is not liable to pay child support for any period prior to the application.

If you are dealing with separation or divorce, the child support system can feel like a lot to take in.

It is more than a money question. It shapes routines, budgets and day to day stability for your family.

Services Australia sits at the centre of the process, assessing and managing payments through a transparent method that applies equally to both parents.

At Unified Lawyers, our Sydney based family law team has guided countless parents through assessments and negotiations, helping them reach fair outcomes while keeping children's interests front and centre.

This guide explains the essentials in clear, practical terms, whether you are likely to pay or receive support.

If your situation is more complex, for example multiple children from different relationships, income earned overseas, or a dispute about care arrangements, tailored advice can save time and stress.

You can book a free consultation with us to talk through your options.

2025 Quick Reference

• Fixed rate : $1,768 per child per year, capped at 3 children per assessment.
• Minimum annual rate : $534 per year for eligible low income payers.
• Costs of Children tables : 2025 tables apply to child support periods starting on or after 1 January 2025, with amounts based on the latest Annualised MTAWE figure.

Understanding Child Support

Think of child support as the way both parents share everyday costs like food, housing, clothing, health and education after separation.

The rules sit in federal law and Services Australia administers them, so there are no state by state quirks to trip over.

Whether you are in NSW or WA, the same calculation rules apply.

The principle is shared responsibility. Often the parent with less care time pays the parent with more care.

That is not a hard and fast rule though. If the higher earner also has most of the care, payments can flow the other way.

The formula adjusts to the realities of your family.

Two main pathways exist :

• Department assessed payments. Services Australia calculates and can collect the payments under the official formula. This is the most common path and it comes with enforcement options if someone falls behind.
• Private agreements. Parents can strike their own deal through a Binding Child Support Agreement ('BCSA') or a Limited Child Support Agreement ('LCSA'). A BCSA requires each parent to get independent legal advice and is enforceable like a court order. A LCSA is the lighter touch but must be at least the assessed amount. Agreements can even specify in kind contributions such as paying school fees. To get the protection of enforcement, register the agreement with Services Australia.

Our team has helped more than 1,000 parents in the past decade set up, negotiate and adjust child support arrangements. In our experience, private agreements suit cooperative co parenting.

When trust is shaky, a Services Australia assessment gives needed structure and backup.

Key Factors That Determine Child Support Payments

The amount is not guesswork. Services Australia looks at a handful of core inputs that paint a fair picture of your circumstances :

• Number of children. More children means higher overall costs and the table scales accordingly.
• Each parent's income. The formula uses both parents' adjusted taxable incomes so the contribution is proportional.
• Percentage of care. How many nights each parent cares for the children matters. Care is grouped into bands that then translate to cost percentages.
• Relevant dependent children. If a parent supports other children from another relationship, their available income is reduced to reflect that responsibility.

These inputs flow into the formula so two families with the same combined income can end up with different results if their care patterns differ.

Methods Used to Calculate Child Support

Australia uses an income shares model. In plain terms, children should benefit from each parent's resources in proportion to capacity to pay.

The standard calculation runs through eight steps :

1. Work out each parent's child support income. Start with adjusted taxable income, subtract the self support amount, then deduct allowances for relevant dependants.
2. Combine incomes. Add both child support incomes to get the total available pool.
3. Find income percentages. Divide each parent's income by the total to get their share of responsibility.
4. Measure care percentages. Calculate the percentage of nights of care per year for each parent and match it to the established categories.
5. Translate care to costs. Use the Care and Cost table to convert care bands into cost percentages.
6. Compute child support percentages. Subtract each parent's cost percentage from their income percentage. A positive number means that parent pays. A negative number means they are already meeting more than their share through direct care.
7. Look up the costs of children. Refer to the Costs of Children table which factors in combined income, number of children and their ages to produce an annual dollar figure.
8. Calculate the annual amount. Multiply the paying parent's child support percentage by the costs of children to set the yearly liability.

Which formula applies in different situations

• Formula 1. One case and both carers are the parents.
• Formula 2. One case with a non parent carer who has at least 35 percent care. The carer's income is not assessed.
• Formula 3. A parent has more than one child support case and there is no non parent carer.
• Formula 4. Multiple cases and at least one involves a non parent carer.
• Formula 5. Assessment uses the income of only one parent where the other parent's income is not available.
• Formula 6. Assessment again uses only one parent's income in other limited scenarios.

Example :

Sarah's adjusted taxable income is $80,000. Tom's is $40,000. Together that is $120,000.

Sarah's income percentage is 67 percent. They share care 50 to 50, so each has a cost percentage of 50 percent.

Sarah's child support percentage is 67 minus 50 which equals 17.

The Costs of Children table for one child under 13 gives about $15,000. Sarah pays 17 percent of $15,000 which is $2,550 per year.

Even with shared care, the higher earner can still pay a contribution.

Complex setups are common.

Self employment, variable income, special needs or multiple cases can push you into the alternative formulas.

The Services Australia estimator is useful for ballpark figures, but it is a guide only : Child Support Estimator.

How Income Affects Child Support

Income drives the assessment. Adjusted taxable income includes taxable earnings, reportable super contributions, foreign income and fringe benefits.

Deductions can apply for things like union fees or prior child support. The idea is to get as close as possible to real capacity to pay.

If income is low, the assessment can fall to the minimum annual rate or even zero if you sit below the self support threshold.

That does not erase the obligation though.

If circumstances change and a later reassessment shows you should have paid more, arrears can accrue.

Services Australia can also apply a notional income if they consider a parent is under reporting or choosing not to work.

Non agency payments, lump sums, and credits

Some payments made directly or to third parties can be credited against your liability if they meet the rules.

• What can count. Direct transfers, third party payments or in kind support like school fees or health insurance, provided both parties agree or the assessment allows it.
• How credits work. Services Australia may credit approved non agency payments against the assessed amount. Keep clear records.
• Lump sums. A Binding Child Support Agreement can include lump sums that are credited each year until the credit is used up.
• Forms. You can report non agency payments using Services Australia form CS1650.

The Role of Custody and Parenting Time

Care arrangements directly offset costs. The percentage of care is calculated on the number of nights children spend with each parent.

As a guide :

• Less than 14 percent of nights is treated as no significant care.
• Between 35 and 65 percent of nights is shared care which reduces or balances payments.
• Over 65 percent is majority care.

These bands matter. A parent with 40 percent care usually pays less than a parent with 10 percent care because they are already covering more day to day costs.

If care patterns shift, the assessment can be updated.

For more detail on how to formalise care, see our guide : Parenting Orders Guide.

Using Online Child Support Calculators

Services Australia provides a free estimator. Plug in incomes, care, and the number and ages of children to get a quick estimate.

It is handy for planning and negotiation.

Pros. Fast, easy and gives everyone a sense check.
Cons. It is not binding and it struggles with complex situations like self employment or overseas income. Treat it as indicative, not definitive.

Do the numbers change each year

Yes.

The self support amount, income bands, fixed and minimum rates, and the Costs of Children tables are indexed and can change on or around 1 January each year.

Your estimate can also move when new tax data lands.

Modifying an Existing Child Support Order

Assessments are not set in stone. You can apply to Services Australia for a change if circumstances shift in a meaningful way.

The law lists 10 possible reasons.

Common examples include :

• High costs to maintain a child's education, medical needs or special needs.
• Significant changes to income or earning capacity.
• Necessary expenses or obligations to support another child or person.
• High costs of enabling time with the child, such as long distance travel.
• Changes in care arrangements, for example moving from shared to majority care.

Objections and reviews

If you disagree with a decision, you can lodge an objection with Services Australia within strict time limits, often 28 days.

If you still disagree after the objection is decided, you may be able to apply to the Administrative Appeals Tribunal for an independent review.

Frequently Asked Questions

1. How is child support calculated in NSW?

The same national formula applies in NSW as elsewhere in Australia.

There are no state based differences in the calculation, although enforcement can involve state courts.

2. How is child support calculated in WA?

Western Australia also uses the national formula. Child support in WA is assessed the same way as in NSW and other states, even though WA has a state Family Court.

3. Do I have to pay private school fees on top of child support?

Not usually. The formula is designed to cover general schooling costs.

If parents agree to private schooling or special extras, that can be included in a private agreement or raised in a change of assessment.

4. What if I pay the mortgage or buy uniforms directly?

Some direct or third party payments can be credited as non agency payments if they meet the criteria and both parties agree.

Keep receipts and lodge the form.

5. When does child support end

Liability usually ends when a child turns 18, or at the end of the school year if they turn 18 while completing secondary school.

In limited situations, adult child maintenance may apply.

6. How Australian child support is calculated compared to other countries

Australia uses a nationally consistent income shares model. Some countries use flat percentages or broad discretion.

The Australian model aims for proportional contributions based on income and care.

7. Can I agree to a different amount privately

Yes. Parents can enter a Binding Child Support Agreement or a Limited Child Support Agreement.

These can set a different amount than the formula outcome.

A BCSA requires independent legal advice for each parent. Agreements can include cash or in kind contributions.

8. What if the paying parent is unemployed

Payments may reduce to the minimum or zero, but arrears can build if there is no reassessment.

Services Australia may also impute income if they suspect deliberate underemployment.

9. How do they calculate child support generally

They use the child support formula.

It weighs income, care time and number of children to produce a fair and transparent outcome.

Talk to Unified Lawyers

Child support matters can be complex, especially when income structures change, care patterns shift, or there are questions about school fees, non agency payments, arrears or a change of assessment.

Our family law specialists help with assessments, objections, binding or limited child support agreements, enforcement and negotiations so your children are supported and your budget is workable.

We have helped more than 1,000 parents resolve parenting and financial issues.

At Unified Lawyers, privacy, efficiency and strategy matter.

We work closely with accountants and tax advisers where income is complex, and we coordinate with Services Australia processes so every dollar and every day of care is properly accounted for.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.