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The Iranian leap year

The Iranian or Persian calendar has about 8 leap years in a 33-year cycle. An extra day is added to the last month in a leap year.

Calculating the leap year

Leap years usually occur every four years. After every six or seven leap years, the Iranian calendar includes a leap year that occurs on the fifth year instead of the fourth year. A period of 2820 years was the base for calculations to establish the frequency of a leap year occurring on the fifth year. At the start and the end of the 2820-year cycle, the vernal equinox takes place exactly at the same time of the tropical year.

The Iranian calendar dates back to the 11th century, when a panel of scientists created a calendar that was more accurate than other calendars at the time. Although some changes have been made to the calendar, it is slightly more accurate than the Gregorian calendar. Compared with the Gregorian calendar, which errors by one day in about every 3226 years, the Iranian calendar needs a one-day correction in about every 141,000 years.

What is a Leap Year and when is the next one?

Leap Day February 29, 2016

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Leap Year in other calendars