Varshitap is traditionally a Jain tap of about 13 lunar months and 13 days, and its parna/end is normally on Akshaya Tritiya (Vaishakh Shukla Tritiya), not on a fixed Gregorian date. ( jainknowledge.com)

So if you start tomorrow, April 21, 2026, the exact end date cannot be fixed accurately from the English calendar alone because Varshitap follows the Jain lunar tithi system. In simple calendar terms, it would finish around 13 months and 13 days later, but the proper parna day should be matched to the Jain tithi. ( jainknowledge.com)

If you want, I can help you understand the traditional Varshitap start and parna rules in a very simple way.