skuddår

Skuddår, in the Nordic languages, refers to a leap year in which an extra day is added to the calendar to keep it aligned with the astronomical year. In the Gregorian calendar, this means that the year has 366 days instead of 365, with February containing 29 days instead of 28.

The need for a leap year arises because the solar year is about 365.2425 days long, not exactly 365 days. To compensate, most years divisible by four are leap years, adding one additional day. However, to correct for overcompensation in centuries, the rule is refined: century years are not leap years unless they are divisible by 400. Thus years such as 2000 and 2400 are leap years, while 1700, 1800, and 1900 are not. This 400-year cycle ensures long-term alignment with the Earth's orbit.

Historically, the concept originated with the Julian calendar introduced by Julius Caesar in 45 BCE, which added a leap day every four years. The Gregorian reform of 1582 refined the rule to reduce drift further and was adopted gradually by different countries over subsequent centuries. In Swedish, Norwegian, and Danish contexts, related terms for leap year—such as skottår or skuddår—reflect the same calendrical adjustment of adding a day to February.

In practice, February 29 exists only in leap years. People born on this date are sometimes called leaplings. Leap years influence scheduling, anniversaries, and administrative matters, and the 400-year cycle ensures the calendar remains synchronized with the seasons over long periods.