Why we apply SIC
If your tax return is amended and there is a tax shortfall, we apply shortfall interest charge (SIC) rather than general interest charge (GIC). This is because taxpayers are usually unaware of a shortfall amount until they receive an amended assessment.
How the SIC is applied
We apply SIC to the tax shortfall amount for the period between when it would have been due and when the assessment is corrected. SIC is incurred in the year you are served a notice of amended assessment.
We update the SIC rate quarterly using a formula set by law.
SIC applies to amended assessments for:
- income tax for the 2004–05 and later income years
- petroleum resource rent tax for the 2006–07 and later income years.
SIC is applied on a daily compounding basis to the shortfall amount.
Payment of the SIC
The due date for payment of the extra tax and SIC is 21 days after the day we issue the notice of the amended assessment. Once the due date has passed, GIC will apply automatically to any unpaid tax and SIC.
Effect of the SIC on income tax
A deduction for a SIC amount that was incurred before 1 July 2025 can only be claimed in the income year that you received the notice of amended assessment that included the SIC amount.
If you claimed a deduction and:
- we remitted the SIC, you must include the remitted SIC amount as interest income in your tax return in the income year that we granted the remission
- you make an amendment that reduces an earlier amendment, you must also include a reduction in the SIC deduction amount in line with the SIC amount that was reduced.
SIC incurred on or after 1 July 2025 can no longer be claimed as a deduction. This also means if the SIC is later remitted, you do not need to include the remitted SIC as interest income in your tax return.
Remission of interest for shortfall periods
You can ask us to remit a SIC amount (and any related GIC) in full or part if there are extenuating circumstances – for example, if we contribute to an error that leads to a shortfall, or if the shortfall amount is paid before the notice of amended assessment issues.
For more information see PS LA 2006/8 Remission of shortfall interest charge and general interest charge for shortfall periods.