Hi

If you only have a week end date and no other joins you can make to other tables to identify when the sales were made this doesn't sound possible I'm afraid..

You could take an average sales per day figure and add that to the previous months figure and deduct from the next but this is still inaccurate.

If possible (and I acknowledge this may not be possible for you) I would change the structure of your table and take it to a transactional level whereby you can identify individual sales..

Someone else may have other ideas however..

Andy