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 2015, Adhik Asadha (extra month before Asadha) was observed from 17 June to 16 July (south-west tradition, where month starts after new moon) or from 3 June to 2 July (north-east tradition, where month starts after full moon). In 2018, Adhik Jyaistha will be from 16 May to 13 June (or 30 April to 29 May if ending the months on the full moon).

The other names for Purushottam Maas are Adhik Maas, Mala Maas ('unclean month'), and Malimmacha. Spellings in the Latin alphabet vary, including purshottam, purushottam, purushottama; adhik, adhika; maal, māla; maas, maasa, mās, māsa, mas, mass. This is the thirteenth month of the lunar calendar.