Paryushan starts on Bhadrapada Shukla Panchami — i.e., the fifth day of the Shukla (bright) half in the month of Bhadrapada. This is the traditional starting tithi for both Digambar and Shwetambar Jains, though minor regional or sect-specific customs may vary in observance.

• In Digambar tradition, the Das Lakshan Parva (Paryushan) begins on this day.
• In Shwetambar tradition, the same starting tithi is commonly observed, with the focus on reflection, Pratikraman, and related rites.

You can read more about Paryushan basics on JainKnowledge if you’d like a detailed overview