In Jain Dharma, Bhagwan Ādināth (Rishabhdev) is not placed in normal historical time like modern figures.

• He was born in the third ārā of the current avasarpinī (descending time-cycle) – that is millions and millions of years ago, far beyond recorded human history.
• So, there is no exact “year” or modern calendar date (like 5000 BCE etc.) given in Jain scriptures.

About the tithi (lunar date) of His Janma Kalyāṇak:

• Scriptures describe that He took birth in Ayodhyā, as the son of King Nābhirāj (Nabhi) and Queen Marudevī.
• Traditional Jain accounts give His janma tithi as the dark half (krishna paksha) of the month of Chaitra, around Ashtamī/Navamī (8th–9th lunar day), depending slightly on the tradition and text followed.

So, in simple words:

Bhagwan Ādināth was born in Ayodhyā, in an extremely ancient age of this world-cycle (long before our known history), on Chaitra Krishna Ashtami/Navami according to the Jain lunar calendar. An exact modern date does not exist in Jain scriptures.