How is it possible to convert Gregorian Calendar to other

Sep 1 2017 9:32 AM

We are developing a project Human Resource management on MVC 5, and using ASP.NET.

How is it possible to convert Gregorian Calendar to other, such as Ethiopian calendar where days in the months are always 30, and also one extra month 13th exist with 5 days that makes it different from Gregorian calendar.