Money Doesn’t Come Without Guidance ...
ATO calculates the PAYG and GST instalment amounts that, as an eligible taxpayer you have to pay and these amounts are printed on your quarterly activity statement or instalment notice.
These instalment amounts are calculated based on the information taxpayers have previously reported. Every year the ATO adjusts PAYG amounts using a formula that considers the expected growth in the Australia's economy, as measured by GDP.
To calculate your PAYG instalments and GST instalment amounts the most recent information is taken from income tax return or GST return.
The changes in the economy is reflected by the PAYG and GST instalment amounts as these reflect your expected tax liabilities for the current income year. Therefore, ATO adjusts the instalment amounts to reflect the expected changes in the economy.
You don’t know your actual tax liability and have to make additional payment at the time of your annual return if your instalment amounts were not adjusted.