As sammy01 has said, the devil is in the details. But on general principles, what they have done is incorrect.
The Child Support Guide (what they call their 'business rules') provides (in summary):
- If an income amount is determined and later found to be lower than the actual amount, then CSA will recalculate the amount payable to the first day of the current child support period. The child support period is whatever date range they've determined, and will be on your assessments; and
- If an income amount is determined and later found to be high than the actual amount, then CSA will apply the new income figure from the next day after the reassessment.
The second scenario is what appears has happened to you. In other words, there should be no back pay. I would anticipate this is another instance of CSA only applying their rules when it works against the payer - and doing something different when they might work in your favour.
As confusing as it is, read here: 2.4.4.60 New Information about Adjusted Taxable Income | Child Support Guide under the heading 'New information about adjusted taxable income'.
Looking at the commentary, and based on what you've said:
- The payee did not lodge their tax return on time (which takes out (a));
- The actual income figure was lower than the amount determined and used previously (which takes out (b));
- Item (c) only applies if they can provide a valid reason why they hadn't lodged their tax return for two years; and
- Item (d) only applies if the payee lived overseas, wasn't required to lodge a tax return and provided the information within a reasonable time.
If these, or other extraordinary circumstances, don't apply, then "the amendment to the assessment will take effect from the day after the assessment was amended, for the remainder of the child support period."
Odds are they're going to argue with you about it. Get it reviewed. You'll likely have to chase it through to the AAT - which is usually where they'll involve their legal department who will likely agree that you were right all along.
The Child Support Guide (what they call their 'business rules') provides (in summary):
- If an income amount is determined and later found to be lower than the actual amount, then CSA will recalculate the amount payable to the first day of the current child support period. The child support period is whatever date range they've determined, and will be on your assessments; and
- If an income amount is determined and later found to be high than the actual amount, then CSA will apply the new income figure from the next day after the reassessment.
The second scenario is what appears has happened to you. In other words, there should be no back pay. I would anticipate this is another instance of CSA only applying their rules when it works against the payer - and doing something different when they might work in your favour.
As confusing as it is, read here: 2.4.4.60 New Information about Adjusted Taxable Income | Child Support Guide under the heading 'New information about adjusted taxable income'.
Looking at the commentary, and based on what you've said:
- The payee did not lodge their tax return on time (which takes out (a));
- The actual income figure was lower than the amount determined and used previously (which takes out (b));
- Item (c) only applies if they can provide a valid reason why they hadn't lodged their tax return for two years; and
- Item (d) only applies if the payee lived overseas, wasn't required to lodge a tax return and provided the information within a reasonable time.
If these, or other extraordinary circumstances, don't apply, then "the amendment to the assessment will take effect from the day after the assessment was amended, for the remainder of the child support period."
Odds are they're going to argue with you about it. Get it reviewed. You'll likely have to chase it through to the AAT - which is usually where they'll involve their legal department who will likely agree that you were right all along.