The amount to be transferred is in the 'Amount to be Paid to Batch' column on the far right of the 'Current Period Summary' screen.
Non-direct debit customers: if you have a balance from the previous month, this will be visible in the Balance Summary below the suppliers listed on the Current Period page. The amount brought forward from the previous period will be displayed.
So, after all authorisations are done, the C/FWD (Carried Forward) column in the Balance Summary will show the amount that needs to be paid, including any outstanding balances from previous periods.