Adhik Maas - Mal Maas - Purushottam Maas
When Surya Sankranti does not occur on a Chandra Mas then it is known as Adhik Maas. This means that when there is no Sankranti between the two phases and is called Adhik Maas. Adhik Maas occurs after a period of 32 months 16 days and 4 hours, that particular year will have 13 months.
Adhik Maas is also known as Mal Maas or Purushottam Maas. During the year of Chandra Maas there are 354 days and 9 hours. Whereas, during the year of Surya Maas there are often 365 days and 6 hours. Hence, the difference between the days of sun and moon become equal because of the occurrence of Adhik Maas.