Chaumasa (Chaumas Chaudas) ends on Kartik Shukla Ekadashi, which in 2025 falls on 3 November 2025. The period for 2025 is from Ashadha Shukla Ekadashi (6 July 2025) to Kartik Shukla Ekadashi (3 November 2025). Some local temples or communities may note small regional variations, but the widely observed dates are as above. You can read more here