When you create a new invoice, or open a previously-submitted invoice, that is associated with a PO, you will see multiple tabs on the top-left of the invoice header. Select the “Purchase Order” tab and click “View PO Associations” on the right side of the pane.

This will open a pop-up window that shows a list of Invoices IN CONCUR that have been billed, or are in the process of being billed, against the PO. You can add these up and compare to the “PO Total” to get a Balance Remaining.

In the example below, the “PO Total” is $4,300 and there is one invoice totaling $2,000, so the balance remaining is $2,300.