I'm assuming that you are using the Instalment Rate method of recording PAYG Instalments (as detailed at the bottom of this page: https://quickbooks.intuit.com/community/GST-and-BAS/Reporting-PAYG-Instalments-on-BAS-and-IAS/m-p/26...).
The "Income for the Period" figure is not automatically calculated from QuickBooks, but the ATO has a handy article that can point you in the right direction as to what figure you should put in that field: https://www.ato.gov.au/General/PAYG-instalments/Getting-your-PAYG-instalments-right/.
Thanks for your quick response. I had a client contact me saying that a figure came up in this field with a lot more than what their income actually was, so wasn't sure where QBO was getting these figures from. Maybe it was a figure they had previously entered in there? Not sure.
Thanks for the clarification! It is likely that the figure pre-populated from the last BAS filed, so it would be best to compare the figure they have now with the figure in the last BAS to see if they need to adjust the amount.