Makar Sankranti is celebrated on January 14, except in leap years when it is on January 15. Because the festival is based on the solar calendar, it falls on the same day each year, unlike other Hindu holidays that are typically based on a lunisolar calendar. The festival marks the entrance of the Sun into the astrological sign of makara (Capricorn) and the beginning of the Sun’s northward journey (uttarayana).
Makar Sankranti was originally a winter solstice holiday. Its date in January now accords with sidereal time, which is measured against stars, whereas solstices are reckoned according to tropical time, which is measured against the location of the Sun. Because of the precession of equinoxes, the date of Makar Sankranti and the date of the winter solstice are no longer the same.