Answer

Chaumasa in 2026 is starting on Tuesday, July 28, 2026, according to the Jain Mandir 2026 calendar, which lists “Chaturmaas Prarambh (Kalash Sthapna)” on that date. ( susjainmandir.com)

Note

In some Jain sanghs, the exact start can vary slightly by local panchang and community observance, so your local temple calendar is the best confirmation. ( jainknowledge.com)