When was Indian Calendar adopted officially?
The National Calendar is based on the Saka Era with Chaitra being its first month. It consists of 365 days in a normal year. It was adopted from 22nd March 1957 along with the Gregorian calendar for the following official purposes: Gazette of India; news broadcast by All India Radio; calendars issued by Government of India; and, Government communications addressed to the members of the public.
Dates of the National Calendar correspond with those of the Greogrian Calendar. Thus, the first day of Chaitra corresponds to 22nd March in a normal year and 21 March in leap year.