Gita Jayanti is the day on which the most important Hindu scripture ‘Bhagvad Gita’ is originated. Gita Jayanti is celebrated on Mokshada Ekadasi, Shukla Paksha Ekadasi in Margashirsha Month as per all Hindu calendars.
As per the legends mentioned in many ancient scriptures, on this day, Lord Sri Krishna explained Bhagavad Gita to King Arjuna during the Kurukshetra war. When Arjuna wanted to leave the battle field by seeing the bloodshed happening during the war, Krishna has come up with Gita teachings. Krishna taught Arjuna, what is birth, life and death and how to do our duties without any hesitation.
Krishna also explained the Karma Siddhanta to Arjuna which is now made popular in western countries with the name of Personality Development and Time Management.
After the teachings of Bhagvad Gita, Arjuna performed his duty of fighting enemies in Kurukshetra war and won over the Kauravas who grabbed the kingdom from Pandavas.
Since then, Mokshada Ekadasi is celebrated as Gita Jayanti. As per some popular beliefs in South India, Kartika Amavasya is also celebrated as Gita Jayanti. According to Sri Ponnaluri Srinivasa Gargeya Siddhanthi (Asthana Jyotishya of Sri Kurthalam Siddheshwara Peetham) who hails from Hyderabad, Andhra Pradesh, there are some calculations of time which gives us Kartika Amavasya as Gita Jayanti.