How your income affects your child support

Find out how we use each parent’s income when we make a child support assessment.

When we work out each parent’s income, we’ll know their share of the children’s costs. We don’t use income from any non-parent carers. Your percentage of care can also affect these costs. Learn about the assessment formula we use.

What income information we use

We base your child support assessment on your income for the financial year that ended before your current child support period. We use your adjusted taxable income.

To make sure we base your child support on the right income, you should lodge your tax return as soon as you’re able to with the Australian Taxation Office (ATO). If you don't need to lodge, you can provide your income online by logging into your Child Support online account through myGov or the myGov app.

If you live overseas, financial year means the financial year of the country you live in. Learn about child support when parents and children live overseas.

What income we use if you haven’t lodged your tax return

If you haven’t lodged your tax return, you need to tell us your adjusted taxable income for the last relevant year. We may ask you for proof of your income. You can update this online by logging into your Child Support online account through myGov, the myGov app or by contacting Child Support on 131 272.

If you don’t, we’ll work out a provisional income for you. We will calculate what we believe your adjusted taxable income is likely to have been, based on information from previous income years.

If you haven’t lodged your tax return for the last financial year and we don’t have enough information, we’ll use your tax return from the year before and adjust it for inflation.

However, if you haven’t lodged your tax return for the year before and we don’t have enough information, we’ll then use either:

  • your last lodged tax return, adjusted for inflation
  • two-thirds of the male total average weekly earnings as your income.

We’ll use the higher of these 2 amounts.

If your actual income was lower than the provisional income we used, we usually can’t go back and change your income at a later date. This means if you pay child support, you may overpay.

If you lodge your tax return late and your actual income is higher than the provisional income we used, you may get a debt or overpayment.

We may make a new assessment when you or the other parent lodges a tax return for the year.

If you need to update your income for a previous financial year we have online help to guide you through the steps.

What income we use if you live overseas

If you live overseas, we won’t know when you lodge a tax return in the country where you live. If you have a child support assessment from us, you need to tell us your last financial year’s income. You must do this at the start of each child support period. You may need to give us proof of your income.

You need to lodge your tax return for that year as soon as possible. Learn about child support when parents and children live overseas.

Tell us your income

As soon as you know your income information, you need to tell us. You can do this before you’re ready to lodge a tax return with the ATO.

If your Child Support online account is linked to myGov you can sign in now to tell us about changes to your income online.

Sign in to myGov

You can also tell us by:

You can also complete the income declaration form and submit it by either of the following:

If there are changes to your income

You must tell us about any changes to your income when they happen. We may need to change your child support assessment. This includes if you stop or start getting an income support payment from Centrelink. We can’t backdate some income changes, so you need to tell us as soon as possible.

If your current income is lower than the income we are using in your child support assessment, you may be able to give us an estimate of your current income.

We can only accept an estimate in certain circumstances. Your current adjusted taxable income must be at least 15% lower than what we’re using in your child support assessment.

One of the following must also apply:

  • the ATO has assessed your income for the financial year we are using for your assessment
  • the ATO hasn’t assessed your income for the financial year used in your assessment, but you’ve declared your income.

Only you can make an estimate. If you choose to make an estimate, it’s important you do it as soon as you can. We can only use your estimate from the day you tell us.

You may not be able to make an estimate if your child support involves any of the following:

When you need to update your estimate

Your income changes

If your income goes up or down, you must make a new estimate of income. If your income goes down, we can’t backdate your estimate. Update your estimate as soon as possible.

Your estimate ends before your child support period

Your income estimate lasts until the end of the financial year. If your child support period continues into the new financial year, you should give us a new income estimate. You need do this before the end of the current financial year.

If you don’t give us a new estimate, we’ll base your assessment on the income from the last financial year.

How to make an estimate

To make an estimate online you need a Child Support online account linked to myGov. To do this, sign into myGov and select Income then Update your current income.

Sign in to myGov

You can also make an estimate by:

You can also complete the Estimate of income for use in Child Support Assessment form and submit it by:

Make your estimate as accurate as you can.

What happens if you don’t update your estimate

After the financial year ends, we compare your estimate to your actual income for the year.

If the estimate is lower, you may have to do one of the following:

  • pay off a debt
  • pay back an overpayment.

What happens if you lodge your tax return late

If you haven’t lodged a tax return on time, we’ll work out your provisional income. If your actual income was lower than your provisional income, we can’t usually go back and change your child support.

Change of assessment

If you have special circumstances, you may be able to apply for a change of assessment.

Special circumstances can include either of these:

  • the financial resources, income and property of either parent aren’t being reflected in the assessment
  • the earning capacity of either parent is greater than what’s reflected in the assessment.

This can include income and financial resources that aren’t part of the adjusted taxable income in the child support formula.

If you don’t need to lodge a tax return and you lodge a non-lodgement advice, you’ll need to tell us. You must do this even if you had no income or you’ve already told the ATO you don’t need to lodge.

You also need to confirm your income for Child Support using your Child Support online account.

If you earn extra income after you separate

If you earn extra income after you separate, you may be able to exclude it from your child support assessment. For example, you might be able to exclude some of the income you earn if you start a second job.

To exclude extra income, you need to show you earned it in a pattern that started after separating. This could be from any of the following:

  • getting a new job on a higher salary
  • opening your business for longer hours
  • getting a second job.

You also need to show you didn’t earn it in the normal course of events. For example, it can’t be from any of the following:

  • a regular pay increase
  • your usual pattern of overtime
  • ordinary seasonal changes in income.

You can only exclude income if all of the following apply:

  • you lived together, and were in a relationship with the other parent for at least 6 months
  • you apply to exclude the extra income less than 3 years after separating
  • you’re still separated at the time you apply.

You may be able to exclude up to 30% of your adjusted taxable income.

Both parents can apply to do this.

To apply to exclude extra income, complete the Application for Post Separation Income to be Excluded form.

You can then upload it using either your:

You can also send it by post or fax.

If you’re a non-parent carer, you won’t need to tell us about income changes.

If you have any questions call the Child Support Enquiry Line.

What to do if you get a letter about a system issue with your child support case

Due to a system error, we may have incorrectly calculated your provisional income used in an assessment from 2008 or after. We'll send letters to you and the other parent if you’re affected by this.

We apologise for not getting your assessment right.

We have not changed your assessment. We need to speak with you and the other parent so we can decide together if your past assessment should be corrected. This includes either the:

  • amount you received
  • amount you paid.

Before we make any changes to your assessment, you may need to consider a few things. If you got Family Tax Benefit Part A during this time, it may affect this. When you call, we’ll help you to understand this too.

If you’ve got a letter and would like to understand how this issue affects you, please contact the Child Support enquiry line. Enter your Child Support ID when prompted.

If we don’t hear from you or the other parent, your assessments impacted by this error won’t change.

Page last updated: 4 June 2026.
QC 27966