Purushottam Maas (translit. puruśottama māsa) or Adhik Maas (translit. adhika = 'extra', māsa = 'month') is an extra month in the Hindu calendar that is inserted to keep the lunar and solar calendars aligned. "Purushottam" is an epithet of Vishnu, to whom the month is dedicated.

The position of Adhik Maas amongst the other months is variable, re-occurring about every 32.5 months. This is in contrast to some other common lunisolar calendars that insert an intercalary lunar month at a fixed point of the year. For example, in the Jewish calendar, the extra month is added before Adar; in the Buddhist calendar, it is added after Ashadha / Waso. During 2018, Adhik Jyaistha (extra month before Jyaistha) was observed from 16 May to 13 June. In 2020, Adhik Ashwin will be from 18 September to 16 October 2020. The other names for Purushottam Maas are Adhik Maas.