Choumasu, or Chaturmas, is the four-month rainy-season period in Jain Dharma.

It is generally observed from:

• Ashadha Shukla Ekadashi to
• Kartik Shukla Ekadashi

In simple words, it usually falls from around July to around November in the English calendar, depending on the Jain lunar calendar each year.

If you want, I can also tell you the Choumasu dates for a specific year.