Short answer:

• Mahavir Janma Vanchan = the ceremonial reading/listening of Bhagwan Mahavir’s birth episode from the Kalpasutra during Paryushan (mainly a Shvetambar practice).
• Mahavir Janma Kalyanak = the actual birth-anniversary of Bhagwan Mahavir (Mahavir Jayanti), celebrated by all traditions.

Key differences:

• Meaning

- Janma Vanchan: “Reading of the Birth.” It is the public recitation of the Mahavir Janma chapter from the Kalpasutra with deep reverence and reflection. - Janma Kalyanak: “Auspicious Birth Event.” It marks the historical/astral moment of the Tirthankar’s birth.

• When it is observed

- Janma Vanchan: During Paryushan (Aug–Sep). In most Shvetambar sanghs it is held on the 5th or 6th day of Paryushan, depending on tradition. - Janma Kalyanak: On Chaitra Shukla Trayodashi (Mar–Apr). This is the day commonly known as Mahavir Jayanti.

• Who observes it

- Janma Vanchan: Primarily Shvetambar tradition (as part of Kalpasutra pravachan in Paryushan). - Janma Kalyanak: Observed by both Shvetambar and Digambar traditions worldwide.

• Focus and purpose

- Janma Vanchan: Scriptural listening (shruta-dhyan), repentance and vows during Paryushan, moral lessons from the Lord’s birth narrative. - Janma Kalyanak: Festive remembrance of the Tirthankar’s kalyanak, cultivating devotion (bhakti) and vows inspired by His life.

• Typical observances

- Janma Vanchan: Kalpasutra pravachan and chant, darshan of illustrated texts, cradle (jhulan) symbolism, austerity and pratikraman atmosphere. - Janma Kalyanak: Abhishek/snan of the idol, Snatra Puja, 108 kalash-abhishek, bhakti, ahimsa rallies, rath yatra, donations and seva.

Notes by tradition:

• Shvetambar: Both are distinct—Vanchan within Paryushan; Kalyanak on Chaitra Shukla 13.
• Digambar: Do not perform “Janma Vanchan” as in Shvetambar Paryushan; they celebrate Mahavir Janma Kalyanak (Mahavir Jayanti) grandly and observe Das-Lakshan Dharma in the Bhadrapad period.

In essence: Janma Vanchan is a Paryushan-based scriptural ritual about the birth story; Janma Kalyanak is the actual birthday celebration of Bhagwan Mahavir.