Leap Year and the Gregorian Calendar

In order to keep the Gregorian calendar, the global majority standard, in synch with the seasonal year, a leap year carries at least one extra day. Without this correction of an additional day, the calendar and the seasons and astronomical events with which it coincides, would drift and as proclaimed by Pope Gregory XIII in 1582, "Easter and Christmas would eventually fall on top of each other."

By the time Julius Caesar took reign, the seasons were no longer occurring during the months they once had. So in 45 B.C. Julius Caesar developed the Julian calendar by modifying the Roman Republican calendar, adding an extra ten days total to the months and replacing the intercalary month of Mercedonius with an intercalary day in February. Caesar chose the last day of the year, February 30th, as Leap Year Day, the intercalary day to be skipped every three out of four years.

Caesar also included a month in honor of himself, Julius/July. Of course in 4 A.D., Emperor Caesar Augustus named the month of August after himself and pulled the last day of February to give his month the 31 days that Julius' month had, resulting in February's 29 days in Leap Years.

The current Gregorian calendar was developed by Pope Gregory XIII in 1582. Leap Day would come to fall on years divisible by 4 but not by 100, except century years that are leap if divisible by 400. This compensates for the fact that the solar year is almost 6 hours longer than 365 days. Gregory also moved the year end to December 31st.

Leap Algorithm (Wikipedia.org)
Pseudocode to determine whether a year is a leap year or not:
if year modulo 400 is 0 then leap
 else if year modulo 100 is 0 then no_leap
 else if year modulo 4 is 0 then leap
 else no_leap

A more direct algorithm:
If ((year modulo 4 is 0) and (year modulo 100 is not 0)) or (year modulo 400 is 0)
  Then leap
  Else no_leap

Famous "Leapies" – Leap Day Babies
1468 Pope Paul III - last Renaissance pope
1792 John Phillip Holland - designed and built the first submarine for the U.S. Navy
1860 Herman Hollerith - American statistician. Inventor of the 1st Electric Tabulating Machine
1904 Jimmy Dorsey - musician, conductor, composer
1908 Dee Alexander Brown II – novelist, "Bury My Heart at Wounded Knee"
1916 Dinah Shore (Frances Rose Shore) - USA, Actress, Singer, Talk Show Host
1960 Heidi Henriksen - The 1st of 3 siblings born on consecutive Leap Days.
1964 Olav Henriksen - The 2nd of 3 siblings born on consecutive Leap Days.
1968 Leif-Martin Henriksen - The 3rd of 3 siblings born on consecutive Leap Days.
1976 Ja Rule - Rapper and Actor

Useless Leap Vocab & Trivia

At 365.2425, the current calendar year is .00031 off from the solar year, adding up to one day over 4000 years. Keep that in mind in your event planning for 4000 A.D.

Leap Second - A second added or removed every few years to adjust for annual drift caused by weather. Scientists have determined this practice to be unnecessary.

Leap Moon - In countries following the lunar calendar, Leap Moon Months are added when the lunar calendar lags behind the solar calendar by more than one month.

Leapies - Leap Year babies

Leapship - Friendship between two Leapies

LeapGramp & LeapGran - Leap Day baby grandparents

Leapophile - Non-leapies who covet and celebrate Leap Day

Leap Year Cocktail - 1.5 oz gin, 0.5 oz Grand Marnier, 0.5 oz sweet vermouth, and a squeeze of lemon. Shake with crushed ice and pour into a chilled cocktail glass.

Odds against being born on Leap Day – 1,506:1

1288 – Scotland allows women to propose marriage to men during Leap Year. According to the law, a man who declined the Leap Year proposal paid a fine ranging from a kiss to articles of fine clothing. Legend states that this tradition stemmed from a complaint by St. Bridget to St. Patrick of Ireland in the 5th Century that women had to wait too long for a man to propose.

An American interpretation of the 1288 Scotland law is Sadie Hawkins Day.

One in five Greek couples chooses to wed on non-leap years to avoid superstition of bad luck associated with marrying in Leap Years.

Technically, Leap Year babies would have to make it to their 116th birthday to celebrate a golden birthday, the birthday when age in years matches the day of the month born.

Leapies born in 1884 had no birthday during their teen years… 1900 was not a leap year.

The character of Frederic from the Gilbert and Sullivan musical The Pirates of Penzance was an orphaned child born on Leap Day.


A leap year (or intercalary year) is a year containing one or more extra days (or, in case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. For example, February would have 29 days in a leap year instead of the usual 28. Seasons and astronomical events do not repeat at an exact number of full days, so a calendar which had the same number of days in each year would over time drift with respect to the event it was supposed to track. By occasionally inserting (or intercalating) an additional day or month into the year, the drift can be corrected. A year which is not a leap year is called a common year.

Leap Year Origins

Originally, the Roman calendar of 355 days carried an extra 22-day month every few years

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