Child support assessment

How your income affects your payment

We consider each parent’s income equally when we make a child support assessment. We don’t use income from non-parent carers.

What income information do we use

We can usually use information about your income from the Australian Taxation Office.

The income we base your payments on is your adjusted taxable income for the last relevant year. This means the financial year that ended before your current child support period.

If you live overseas the last relevant year is the last financial year of the country you live in. Read about child support when parents and children live overseas.

If you haven’t lodged your tax return for the last relevant year

We’ll work out a provisional income for you. This is what we think your adjusted taxable income is likely to have been.

You need to give us your income details for that year as soon as you can. You shouldn’t wait until you lodge your tax return.

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

If you need to tell us your income

If you haven’t lodged a tax return, you should tell us your income as soon as you can by:

Income from Norfolk Island

If you earned income on Norfolk Island in 2015-16, you can tell us by filling in an income declaration - Norfolk Island income for the 2015-16 financial year form.

If you think we’ve got the other parent’s income wrong

You can tell us if you don’t think we’re using the right income for the other parent.

We’ll look into it and update the assessment if necessary.

If your income is less

Contact us to discuss what you can do.

You may be able to use an estimate of your income for this financial year instead.

How income affects your assessment

We add both parents’ incomes together. Then we work out each parent’s share of the total income. This tells us their share of the children’s costs.

You may be meeting some or all of these costs by caring for the child.

Read how your percentage of care affects your payments.

Read about the assessment formula.

Keep your income details up to date

Lodge your tax return

To make sure we base your child support on the right income, lodge your tax return on time every year.

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 last financial year’s income at the start of each child support period. You’ll need to give us proof of your income. Read about child support when parents and children live overseas.

If your income changes during the year

You should tell us about any changes to your income when they happen. We may be able to change your child support assessments.

If your current income is less than your income from the last relevant year, you should contact us.

Normally we can’t backdate the change, so tell us as soon as you can.

Estimate your income

Your income may have changed since your last assessment. If so, we may be able to use an estimate of your income for this financial year instead.

You can give us an income estimate if:

  • the Australian Taxation Office has assessed your income for the financial year used in your assessment, or
  • you haven’t lodged your tax return for the financial year used in your assessment, but you have declared your income for that year to us, and
  • your current adjusted taxable income is at least 15% lower than that amount

What may be different

You may not be able to lodge an estimate if your child support is based on:

How to lodge an estimate

Fill in the Estimate of income for use in Child Support Assessment form.

You can do this using your Child Support online account through myGov.

Make your estimate as exact as you can.

If you get it wrong you may end up with a debt.

Updating your estimate

If your income changes

If you’ve made an estimate, you must make a new one if your income goes up or down.

Do this as soon as you can. If your income goes down, we can’t backdate it.

If your estimate ends before your child support period

Your income estimate lasts until the end of the financial year. Your child support period may continue into the new financial year.

If this happens you should give us a new income estimate. Do this before the end of the current financial year.

If you don’t lodge a new estimate we’ll base your assessment on the income we used before your first estimate.

When we know your actual income

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:

  • pay off a debt, or
  • pay back an overpayment

Provisional income

If the Australian Tax Office hasn’t told us what your income was for the financial year, we base your payments on provisional income.

How we work out your provisional income

You can tell us your adjusted taxable income for the most recent financial year. We’ll use this if we think it’s likely to be right.

If not, we’ll use any information we can get about your income for that year. You’ll still need to tell us if it’s right.

If we don’t have enough information about last year we’ll use your tax return for the year before that. We’ll adjust it for inflation.

If you don’t have a tax return for that year we’ll use your most recent tax return and:

If you don’t have a tax return for any year we’ll use two-thirds of the male total average weekly earnings.

If you lodge your tax return late

If your actual income was lower than your provisional income we can’t go back and change your past child support. If you haven’t lodged a tax return on time and we work out a more accurate provisional income, we also can’t go back and change your past child support if it’s lower. We may be able to backdate in exceptional circumstances.

Read about exceptional circumstances on the Department of Social Services website.

Change of assessment

If you have special circumstances you may be able to apply for a change of assessment for the time when we were basing your payments on the higher income.

There are time limits for applying, so contact us as soon as you can.

Extra income after you separate

If you earn extra income after you separate from the other parent, you may be able to leave it out of your child support assessment.

Both parents can apply to do this.

How to apply

Fill in the Application for post separation income to be excluded form.

You need to show:

  • you earned the extra income in a pattern that started after separating. This could be:
    • getting a new job on a higher salary
    • opening your business for longer hours, or
    • getting a second job
  • you wouldn’t have earned it in the normal course of events - for example it can’t be from:
    • a regular pay increase, or
    • your usual pattern of overtime


You can only exclude income for 3 years after separating.

No matter how much extra income you earned, you can’t exclude more than 30% of your adjusted taxable income.

Page last updated: 1 August 2018