Purnimanta calendar is followed in most of the North Indian states, like Uttar Pradesh, Madhya Pradesh, Bihar, Punjab and Haryana. In the other states Amanta lunar calendar is followed. Usually, most of the festivals in Purnimanta and Amanta and lunar calendars fall on the same day. However, Vat Savitri Vrat may be taken as an exception.
As per Purnimanta calendar, Vat Savitri Vrat is observed on Jyeshtha Amavasya, which coincides with Shani Jayanti. According to Amanta calendar Vat Savitri Vrat, also known as Vat Purnima Vrat, is observed on Jyeshtha Purnima.
Due to this difference, the married women in Maharashtra, Gujarat and southern Indian states observe Vat Savitri Vrat 15 days later than it is celebrated in North Indian. However, the legend behind the fast remains the same in both cases.
Legend says that Savitri tricked Lord Yama, the lord of death, by asking intelligent questions to Him which forced him to return the life of her husband Satyawan. Hence married women observe Vat Savitri Vrat for the long life and well-being of their husband.