The lunar calendar adds one extra month every third year. This extra month is known by various names: Adhik Maas, Mal Maas, Purushottam Maas, Malimmacha. This is the thirteenth month of the lunar calendar.
Just as there is the lunar year with the extra month (Adhik Maas), so is there a lunar year with a diminished or reduced month, with only eleven months in the year. The lunar year comprising of eleven months only is very rare indeed. It occurs once in 140 years or once in 190 years. But the extra month or Adhik Maas comes every third year. Adhik Maas adopts the name of the month that follows adhik Maas.
Religious Significance Of Adhik Maas
Regarding Adhik Maas (Mal Maas) Hemadri says that Mal Maas Vrat (Adhik Maaas Vrat) is capable of washing away all the sins of people (who observe the Vrat). During this month mukta, nakta, fasting etc are undertaken and garments etc. are distributed to charities. A beautiful story relates to how, in ancient times, through the observance of Mal Maas Vrat, king Nahush was released from all bondage and acquired the throne of Indra (the ruler of gods in heaven).
It is written in the Devi Bhagavat that charitable and meritorious acts and fastings etc. carried out during this Mal Maas (Adhik Maas), inevitably produce results. Just as atomic sized contents within a seed produce a giant and long living Banyan tree, so in the same manner even a little charitable act has done during Mal Maas (Adhik Maas) produces big results.
The Puranas also sing high praises about Adhik Maas and indicate Puja, readings of scriptures etc. during Adhik Maas. Selfless actions, without the expectations of results, are to be performed during Adhik Maas. Mal Maas (Adhik Maas) is the month for Vishnu puja. The recitation of Srimad Bhagavat Purana and of the Bhagavad Gita during this month produces top meritorious results. In addition to singing and listening to the praises of the Lord (Vishnu), undertake Adhik Maas Vrat also. This Vrat is to begin from the first day and ends on the last day of Adhik Maas. Waking up during the hours of Brahma Muhurta (between 4 am and 6 am), after ablutions, place a murti of Radha-Krisha or Lakshmi-Narayana and perform Sodashopachara puja. If there is a temple nearby then perform puja of whatever deities are usually worshipped therein. During the entire month of Mal Maas Vrat eat Sattvic food (vegetarian meals, milk, fruits, nuts, grains, vegetables). One meal at night is recommended.
It is written in the Bhavishyottar Purana that Sri Krishna Himself has said regarding Adhik Maas Vrat that by carrying out the Vrat with the sole aim of worshipping God, through fasting, cleanliness, charity, puja etc. merits are acquired which produce unfailing results and all sorts of calamities are overcome.