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Free · ATO

ATO GIC & SIC Interest Calculator

Enter the amount and dates. The calculator applies the ATO's published rate for every day in the period and compounds it daily, the way the ATO does.

In short: What's the difference between GIC and SIC?

GIC applies when tax or another amount is unpaid after its due date. SIC applies instead when your income tax assessment is amended and there's a shortfall, because you usually didn't know about it; it's lower — the base rate plus a 3% uplift.

Last reviewed against 2 official sources.

Try an example:

The amount and period

GIC charged

$550.39

181 days, compounding daily · total $10,550.39

Current rate (Oct–Dec 2026): 11.51% a year.

How the debt grows with interest

$10,000.00 becomes $10,550.39 by Jul 26, because the charge compounds daily.

The link holds your numbers in the address. Nothing is sent to us.

How the charge is worked out

  1. Find the annual rate for each day's quarter.
  2. Divide by the days in that calendar year to get the daily rate.
  3. Apply it to the balance including interest already charged, daily compounding.

Worked example

A$10,000 was due on 1 January 2026 and paid on 1 July 2026. Rates were 10.65% (January–March) and 10.96% (April–June). Over 181 days the GIC comes to about A$550.

Limits

  • Rates are built in from July 2021 to December 2026; outside that the nearest rate is used and flagged.
  • Part payments reduce the balance; this calculator assumes one amount for the whole period.

Reading the charts

Each chart redraws as you change the inputs and uses the same calculation as the result above. Choose "Show data" for the exact figures as a table, or download them as a CSV. "Copy link" saves your numbers in the page address so you can come back to the result or share it; nothing is sent to us.

Official sources

Figures last reviewed .

Frequently asked questions

What's the difference between GIC and SIC?

GIC applies when tax or another amount is unpaid after its due date. SIC applies instead when your income tax assessment is amended and there's a shortfall, because you usually didn't know about it; it's lower — the base rate plus a 3% uplift.

How is GIC calculated?

Daily, compounding. The daily rate is the annual rate divided by the number of days in the calendar year, and the rate changes every quarter.

What are the current rates?

For October to December 2026: GIC 11.51% and SIC 7.51% a year.

How often do the rates change?

Every quarter. The ATO generally announces the next quarter's rates about two weeks before it starts.

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Disclaimer: This tool gives a general estimate based on what you enter and the published rules. It is not tax, legal or financial advice, and the tax authority makes the final decision. Speak to a qualified professional before acting. See our disclaimer.