How to know what day will come chatt in varshitap

In Varshitap, the day does not depend on the weekday like Monday or Tuesday. It is counted by the Jain lunar tithi and by the sequence of fasting/rest days in your sankalp.

If by “chatt” you mean “chhath” / the sixth day, then:

• Start counting from the day you began Varshitap.
• Follow the tithi-based Jain calendar.
• The exact day can change because Jain observances follow lunar dates, not only the English calendar.
• For exact determination, check the Jain Panchang or ask your guru/pravachan guide.

Simple rule:

• Count according to tithi
• Do not count only by weekdays
• Sunrise and tithi change are important

If you want, I can also explain the full Varshitap counting method in a simple day-by-day way.