When you set up a new Customer (Debtor) in QuickBooks, there is the facility to add an opening balance to the customer record, as at a date that can be selected from the calendar.
By entering a figure on the customer record, what QuickBooks is doing behind the scenes, is generating an invoice. This invoice can somewhat be edited, the name, the date, the amount etc but a tax code cannot be added to the tax column.
If the business is registered for GST on an accruals basis, this is fine because the GST would have been picked up in the previous accounting system. However, if the business is registered for GST on a cash basis, then once this invoice is paid, the GST should be reported – and the GST figure is not split from the total sale.
Another point to consider is that the opening balance may be made up of more than one outstanding invoice and may cause havoc if the customer is paying per invoice, reducing the one opening balance amount, but having no concept of aging of the debtor, or individual invoice totals. Instead of using the opening balance feature on the customer record, create a QuickBooks item called OB (opening balance) positing appropriately in the general ledger. Redo any outstanding invoices in the new data file, using a single line item (OB) to pick up each invoice as at the date that it was originally generated. If the business is registered on a cash basis, add the appropriate tax code to the tax column. There is no need to add the tax code if the business is registered for GST on an accruals basis.
There would still be original documentation, so not much detail is required when the invoice is reentered. This would then give accurate aging reports as well as reporting the GST on sales correctly.