Common year

{{Short description|Calendar year with 365 days}}

{{about||the calendar era|Common Era|the fictional date system|Common Year (Greyhawk)}}

{{Use mdy dates|date=April 2025 |cs1-dates=ll}}

A common year is a calendar year with 365 days, as distinguished from a leap year, which has 366 days.{{Cite web |title=Year {{!}} Calendar, Astronomy & Timekeeping {{!}} Britannica |url=https://www.britannica.com/science/year |access-date=January 27, 2025 |website=www.britannica.com |language=en}} More generally, a common year is one without intercalation. The Gregorian calendar, used by the majority of the world, employs both common years and leap years. This is to keep the calendar aligned with the tropical year, which does not contain an exact number of days. A common year is approximately a quarter day (six hours) shorter than a tropical year, which has 365.24 days.{{Cite web |title=Leap Day on February 29 |url=https://www.timeanddate.com/date/leapyear.html |access-date=January 27, 2025 |website=www.timeanddate.com |language=en}} If the Gregorian calendar only used common years and omitted leap years, the calendar would be out of sync with the tropical year by approximately 24 days in 100 years.{{Cite web |first1=Zulficar |last=Abbany |date=February 28, 2020 |title=No perfect calendar: Why we have leap years|url=https://www.dw.com/en/no-perfect-calendar-why-we-have-leap-years-and-why-the-earths-always-out-of-sync/a-19077064 |access-date=April 8, 2025 |website=dw.com |language=en}}

In the Gregorian calendar, 303 out of every 400 years are common years. Leap years are any years that are divisible by 4, unless it can also be divided by 100, in which case it is a common year. One exception is if the year can be divided by 4, 100, and 400 - these years are leap years. The extra common years are added to account for the fact that common years are 5 hours, 48 minutes, and 46 seconds shorter than a tropical year, rather than six hours exactly. By comparison, in the Julian calendar, 300 out of every 400 years are common years, with every fourth year being a leap year without exception.

The common year has 52 weeks and one day, hence a common year always begins and ends on the same day of the week (for example, January 1 and December 31 both fall on a Wednesday in 2025) and the year following a common year will start on the subsequent day of the week.{{Cite book |last=Lardner |first=Dionysius |author-link=Dionysius Lardner |url=https://books.google.com/books?id=M6UWAQAAIAAJ |title=The Museum of Science and Art |date=1855 |publisher=Walton and Maberly |pages=23 |language=en}} In common years, February has exactly four weeks,{{Cite web |title=Weeks in a year |url=https://www.math.net/weeks-in-a-year |access-date=January 28, 2025 |website=www.math.net}}{{Cite book |last=Kramer |first=Michael S. |url=https://books.google.com/books?id=5IbrEAAAQBAJ |title=Believe It or Not: The History, Culture, and Science Behind Health Beliefs and Practices |date=December 28, 2023 |publisher=Springer Nature |isbn=978-3-031-46022-7 |pages=195 |language=en}} so March begins on the same day of the week as February does. November also begins on this day. For example, February 2025 began on a Saturday, thus March 2025 also began on a Saturday. November 1, 2025, will also start on a Saturday.

Each common year has 179 even-numbered days and 186 odd-numbered days.