Schrikkeljaren

Schrikkeljaren, or leap years, are calendar years that contain an extra day to keep the solar year in alignment with the calendar. In the Gregorian calendar, which is used by most of the world today, a standard year has 365 days, while a leap year has 366 days, with the additional day inserted as 29 February. The need for leap years arises because the Earth’s orbital period around the Sun is approximately 365.2422 days, a fraction that cannot be expressed as an integer number of days.

The modern rule for determining leap years was introduced by Pope Gregory XIII in 1582 as part of the Gregorian reform. According to this rule, a year is a leap year if it is divisible by four, except for years that are divisible by 100, unless they are also divisible by 400. Consequently, 2000 and 2400 are leap years, whereas 1900, 2100, and 2200 are not.

Historically, the Julian calendar, implemented by Julius Caesar in 45 BC, added a leap day every four years without further exception, resulting in a discrepancy of about three days every four centuries. The Gregorian correction reduced this drift, improving long‑term calendar accuracy.

Culturally, leap years have generated various traditions and superstitions. In some regions, women may propose marriage to men on 29 February, a practice known as “leap day” proposals. In the Netherlands, the term “schrikkeldag” is sometimes used for this date, and the surname “Schrikkeljaren” can be found, historically linked to families whose ancestors were born on a leap day.

Leap years also affect legal and financial matters, such as the calculation of interest, rent, and age‑related rights, requiring specific adjustments in contracts and statutory provisions to account for the extra day.