Customised date calculator for Wordpress.

I need a specialised date calculator for my wordpress website. The types of functions this calculator will need to perform are, including, but not limited to: > 'x' amount of days from a set date; > 'x' amount of Business Days (i.e. not including weekends and UK Bank holiday days); > 'x' amount of days, starting from the next day; > 'x' amount of Clear Business Days (i.e. not including the first of the last day of the period); An example of a similar calculator can be found at the following website (I am hoping for something that will look and feel similar). [login to view URL] I am hoping that this could be created by inputting lines of code into my wordpress page template. Please feel free to reply with suggestions. Many thanks