Sometimes is very important to find when the next day of the delivery is or how many days business passed between current date and desirable date of our client to see his/her goods. Very often we need to develop client - validation (read: develop it in JavaScript). In this article I demonstrate two the most important functions for calculation business days between dates and find particular business day in the future. This program is very flexible and can be adapted to any country (because it is required to set up weekends days and holidays). At the end I will show how this data can be filled into MS SQL Server database (England UK public holidays till 2014).