Hi Adnaan,
Please use the HijriCalendar class which belongs to the System.Globalization namespace for converting Gregorian DateTime to Hijri.
C#
System.Globalization.HijriCalendar hc = new System.Globalization.HijriCalendar();
DateTime hijriDate = new DateTime(hc.GetYear(DateTime.Now), hc.GetMonth(DateTime.Now), hc.GetDayOfMonth(DateTime.Now));
VB.Net
Dim hc As System.Globalization.HijriCalendar = New System.Globalization.HijriCalendar()
Dim hijriDate As DateTime = New DateTime(hc.GetYear(DateTime.Now), hc.GetMonth(DateTime.Now), hc.GetDayOfMonth(DateTime.Now))