February 29th is Leap Year Day or Leap Day, and only occurs in Leap Years, which is typically every four years. The day is added to the calendar in this manner to keep synchronized with the astronomical or seasonal year. The opposite of a Leap Year is a Common Year and Common Years are missing out on that extra day in February! The t-shirts here for Leap Year Day are great for those who have a rare February 29 birthday, anniversary, or have another significant milestone that took place on that day.