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# How often do calendar dates repeat?

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Calendar dates repeat regularly every 28 years, but they also repeat at 5-year and 6-year intervals, depending on when a leap year occurs within those cycles, according to an article from the Sydney Observatory. Repeating calendar dates are also affected by the adjustments made for leap years at the end of each century.

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The calendar dates of leap years within the same century only repeat every 28 years, but the calendars of non-leap years repeat more often than that. For example, as shown by Timeanddate.com, the calendar for the year 2000 repeats every 28 years until 2084, but the calendar for 2001 repeats 6 years later in 2007, 17 years later in 2018 and 28 years later in 2028. The cause of these varying cycles of repetition is the fact that while the date usually advances by one weekday every year, it advances two weekdays on a leap year. This pattern can be illustrated by an example: The year 2000 starts on a Saturday, and without any leap years, the year 2007 would also start on a Saturday. However, since 2000 and 2004 are both leap years, the year 2007 starts two weekdays later, on a Monday. Any two years that are not leap years and begin on the same day of the week will share the same calendar dates.

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## Related Questions

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Differences between the Julian and Gregorian calendars include the date for the start of the new year, different approaches to leap years and different amounts of discrepancy with the solar year. The Gregorian calendar came about, in part, to help the Church more accurately determine the date of Easter.

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The Gregorian calendar repeats itself in 28-year cycles. A calendar for a particular non-leap year repeats itself after 11 years twice and repeats itself after six years once in a 28-year span. Calendars for leap years repeat themselves every 28 years.

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According to the Guinness World Records organization, the Jewish Calendar, which has been in use since the 9th century C.E., is the oldest calendar still in popular use. This calendar is used to determine the dates of Jewish holidays such as Rosh Hashanah and Yom Kippur.