Software: Intuit QuickBooks
When creating a general journal, you can only associate a tax (GST) amount to the tax account (GST Payable account), the taxable amount will not be able to associate with the tax account.
If you were to make a general journal of:
Debit Expense 1000.00
Debit GST Payable account 70.00
Credit Bank 1070.00
The Tax Agent (in the Name column) will be automatically associated with the tax account (GST Payable account) as according to your tax (GST) setting. Besides, you can select the relevant Tax (GST) Item at the Tax Item column.
The debit of 70.00 to the tax account (GST Payable account) will be updated in the Tax Agency Report (GST).
If you intend to associate income or expense account with tax (GST), you should consider using an Invoice, Bill or Write Cheque transaction type instead of a General Journal. From the above example, the debit of 70.00 to the tax account (GST Payable account) is the tax amount and will be updated at the amount column of the Tax Agency Report; the taxable amount in the report is blank, you may consider to export the report to Excel and calculate backward to obtain the taxable amount.