flag up message if a date is missed

Hi,

I have a tracking system in excel where I've got a planned and an actual date for each stage in a project so each stage has to be done in order.

At several points in the project, meetings are set up accordingly: in the Second Tuesday of every 4 week period. So at the start of the project a provisional date is set up for each meeting.

I want a message box or something like it to display "Please review meeting date" , if that scheduled meeting has been missed.

Is there a way of doing this?

Any help would be much appreciated

Many thanks
Harry

great idea! didn't think of that

Data validation kind of works but I want the message to display all the time and not just when I click on the cell?