The first day of spring occurs on March 20 in the Northern Hemisphere, 79 days after the first day of the year. During leap years, when the month of February has 29 days instead of 28, the first day of spring falls on the 80th day of the year.
In some years, the first day of spring, or the vernal equinox, falls on March 21, though this is exceptional. While 36 out of 100 vernal equinoxes occurred on March 21 during the 20th century, all of the vernal equinoxes in the 21st century are on March 20 or earlier. In the Southern Hemisphere, the vernal equinox usually falls on September 22, or 265 days after January 1 in non-leap years.