I got a question about excel and/or access table

Good day all experts,
I got a question about excel and/or access table preferably 2003 version but if there is a lot of difference between the 2007I would like a solution to:
I try to compare 1 date field and want to fill in a second date field that calculate the different the first date + 1 month and fill in another field with a Yes/No option in that row.
So this is to calculate an invoice date + 1 month to receive the date overdue in another date field.
I use the yes/no to do further calculations to merge and send out letters for those overdue.
Table 1 Table 2 Table 3 Table 4 Table 5
Invoice date: Date overdue: Amount overdue: Letter to send: Send date
09/06/22 ? 100 Yes/No? ?
I hope this all is clear!

Tanks theoriginalinvisible,

It helped very much...just had to replace , by ; and it worked.
Any idea how to flag field to be on/off or yes/no depending on that due date? versus invoice date?

I try to compare 1 date field and want to fill in a second date field that calculate the different the first date + 1 month (THIS IS SOVED BY YOU) and then in a third field trigger an option field with a Yes/No or 1/0 or on/off option in that row depending if the field date overdue is true.
Thanks for helping me out.

Chris

Attached test xls files

Table 1 Table 2 Table 3 Table 4 Table 5
Invoice date: Date overdue: Amount overdue: Letter to send: Send date
09/06/22 ? 100 Yes/No? ?

Now i know i never been a programmer or im lazy or plain stupid...lol Thx lee