Adhik Mas is unique to the traditional Hindu lunar calendar that is based on the cycles of the moon. According to the Hindu Lunar calendar, the moon takes about 29.53 days to revolve around the earth. This makes lunar month 29.53059 days only. Adding all these 12 lunar months the year will have only 354.36708 days while the Solar year is about 365 days. To adjust lunar months to the solar year, the Lunar calendar adds one extra month every third year. The word Adhik means extra, hence, the Adhik month is basically an extra month that comes once every 3 years. The position of this month is not fixed and it can occur between any two months randomly. In 2020 Adhik Mas is from 18th September to 16th October is the most auspicious month of 2020.
During this period, marriages, tonsures (mundan), inaugurations of new home, fasting with a desire of some worldly gains, buying new ornaments and vehicles are prohibited. In a book called Purushottama Granth, also called Purushottam maas Mahatyam, many aspects of the special religious significance of this month are found.
This month is also called the month of Purushottam (i.e. Purush Uttam, which means ‘Elevated Soul or Being). This month is the best time of the year to work on ourselves and speed up our spiritual evolution and realise the perfection of our being. Spiritual evolution means becoming free of limited body and role consciousness and function from the most elevated level of soul consciousness (ie Purushottam).
According to legend, there were 12 lunar months and each was assigned to 1 god. Rishi-Munis calculated and facilitated Purushottam Mas to balance solar and lunar years. Since it is Maal (unclean or by-product) Maas, therefore, no God agreed to become the deity of the month. Lord Vishnu was then approached. Lord Vishnu took pity and assigned Maal Maas to himself, hence justifying the significance of this holy month.