Agrahayana is one of the lunar months as per the Hindu calendar. According to the India's national civil calendar, Agrahayana is the ninth month of the year. This lunar month starts on November 22 and ends on December 21. This month was also known as Maargashirsha after the nakshatra Mrigashira during the Vedic period.

The meaning of the term Agrahayana is 'ayan' or equinox. It is thought that this name may have been given when the sun was near Orion at the time of vernal equinox, i.e. around 7000 years ago. It is thought due to the close relation of this name with the Mrigashira asterism. As per the lunar religious calendars, the month of Agrahayana may start on either the new moon or the full moon around the same time of year. The month initiates with the Sun's entry into Scorpio as per the solar religious calendars.