If you have business or investment income, you must pay instalments towards your income tax liability. However, you do not have to do so unless the Commissioner has given you an instalment rate. Generally, instalments are payable for each quarter of your income year. Alternatively, instalments could be payable monthly or annually.

Your instalments may be based on your previous year ' s income tax liability and notified to you by the Commissioner, or on your estimate of your income tax liability for the current income year. (In this case, you are a quarterly payer who pays on the basis of GDP adjusted notional tax). Generally, four quarterly instalments are payable annually on this basis, but you may only be required to pay two.

If you are not eligible to pay instalments on that basis, or if you are so eligible but choose not to do so, you must work out the amount of your quarterly instalment by multiplying your instalment income for an instalment quarter by the rate the Commissioner gave you, or by a rate you choose yourself. (In this case, you are a quarterly payer who pays on the basis of instalment income).

If your business or investment income exceeds a certain limit, you may have to pay an instalment after the end of each month. (In this case, you are a monthly payer).

If you are not required to be registered for GST purposes, you may be able to choose to pay an annual instalment after the end of the income year. (In this case, you are an annual payer).

The amount of annual instalment can be your instalment income for the income year multiplied by the rate the Commissioner gave you, or an amount based on your previous year ' s income tax liability and notified to you by the Commissioner, or your own estimate of your income tax liability for the income year.