In Jainism, Chaumās / Chāturmās is a time period, not a single day.

When is it?

• It starts: around Ashādh Shukla 11 (Devshayan Ekādashi)
• It ends: around Kārtik Shukla 11 (Prabodhini Ekādashi)
• In the English (Gregorian) calendar this is usually from about July to about November.
• Exact dates change every year because they follow the lunar calendar.

What happens in Chāturmās?

• Jain sadhus/sādhvīs (monks & nuns) stay in one place (do not travel), because of the rainy season and to avoid himsā (violence to tiny living beings).
• Many Jains take special vrats and follow more discipline in food, speech and conduct during these months.

If you tell me the specific year you want (e.g., 2026), I can explain roughly which dates it will fall between in that year.