Spreadsheet look up list?

I have a spreadsheet that takes a date and by adding 7 each time creates a list of 10 dates for interviews. What I would like to do is have it look up a separate list of dates and check if that date is on the list of dates and if it is I want to to add another 7 days. It basically checks to see if the date is a bank holiday. I know how to set up the 'look up list' but cant work out the syntax of the formula needed. Thanks for any help guys. - Mark