Forecasting

Hi, I have some data which shows invoices which are approved for payment in our system and their due dates. We are looking to forecast what will be paid on a particular payment run. So we work with several different regions i.e. UK, US, Singapore, Australia and they all have payment runs on different days. As an example, we are currently making payment for UK on Tuesday and Thursday and including anything that was overdue and due up until the next payment run. so for a payment run today, this would pay anything that may now be approved and overdue with a due date up to Tuesday 5th May. what will be the best way to do this? I have a separate table showing the days of the payment runs and a table with the total values approved.