No, it is not absolutely compulsory to do chovihar (eating and drinking only till sunset / avoiding food and water at night) on the day before upvaas (fast).

But there are some important points:

1. Ideal / Shreshth Aachar (best practice)

- Doing chovihar regularly is itself a very good Jain discipline. - If you know that you are going to do upvaas tomorrow, then doing chovihar the previous evening is considered very good and discipline-enhancing, because: - It prepares the body and mind. - It reduces attachment to taste and routine eating. - It supports samyak tapa (proper austerity).

1. Not a condition for validity of Upvaas

- Your upvaas is valid and religiously acceptable even if you did not do chovihar the previous day. - There is no rule that “without chovihar one day before, upvaas does not count.”

1. When it becomes more important

- For those who have taken specific vows (pachakhan), like: - “Whenever I do upvaas, I will surely do chovihar one day before,” then for that person, it becomes personally compulsory because of their own vow. - For others, it remains suprasansa-niya aachar (highly praiseworthy conduct), not a strict compulsion.

1. Practical guidance

- If your health allows and family situation permits: - Try to make a habit of daily chovihar, or at least - Always do chovihar the day before planned upvaas / beyasi / tivihar etc. - If sometimes you cannot do it due to health, travel, or strong practical reasons, you can still do upvaas with shraddha and pratikraman for any shortcomings.

Summary:

• Compulsory? – No, as a general rule, it is not compulsory.
• Recommended? – Yes, it is strongly recommended and considered shreshth (best practice) before upvaas.