Need help with forecasting spreadsheet

I've been trying to create a spreadsheet for forecasting department performance. Needless to say it's been causing me some frustration. I'll try explain it as best I can;

We receive batches of emails & letters daily to be processed. The values concerning us here are the Date & the Total for the date.

Inevtiably work will be left over from the previous day which will need to be added onto the total.

We assume an average output of 5 processed per hour.

Working hours vary (Staff may be ill, holidays, other tasks...), but we assume 35 hours daily is spent on task.

We are usually lagging up to 2 weeks behind the current date.

The spreadsheet should be able to tell us what date we will be processing each batch on.


I'll try knock up an example of what I had in mind & attach it to this post. Hopefully some Excel experts out there will understand what I need I know it should be possible to do, but my searches aren't paying off at the moment.

Attached are the "Old" forecast spreadsheet (Which I don't understand the fucntioning), the other is the current worksheet used, which isn't particularly good enough.