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Calendar for any common year starting on Wednesday,  




 



 




ISO 8601conformant calendar with week numbers for  




 



 




In the (currently used) Gregorian calendar, alongside Sunday, Monday, Friday or Saturday, the fourteen types of year (seven common, seven leap) repeat in a 400year cycle (20871 weeks). Fortythree common years per cycle or exactly 10.75% start on a Wednesday. The 28year subcycle only spans across century years divisible by 400, e.g. 1600, 2000, and 2400.
Decade  1st  2nd  3rd  4th  5th  6th  7th  8th  9th  10th  

16th century  prior to first adoption (proleptic)  1586  1597  
17th century  1603  1614  1625  1631  1642  1653  1659  1670  —  1681  1687  1698  
18th century  1710  —  1721  1727  1738  1749  1755  1766  1777  1783  1794  1800  
19th century  1806  1817  1823  1834  1845  1851  1862  1873  1879  1890  —  
20th century  1902  1913  1919  1930  —  1941  1947  1958  1969  1975  1986  1997  
21st century  2003  2014  2025  2031  2042  2053  2059  2070  —  2081  2087  2098  
22nd century  2110  —  2121  2127  2138  2149  2155  2166  2177  2183  2194  2200  
23rd century  2206  2217  2223  2234  2245  2251  2262  2273  2279  2290  —  
24th century  2302  2313  2319  2330  —  2341  2347  2358  2369  2375  2386  2397 
400 year cycle
century 1: 3, 14, 25, 31, 42, 53, 59, 70, 81, 87, 98
century 2: 110, 121, 127, 138, 149, 155, 166, 177, 183, 194, 200
century 3: 206, 217, 223, 234, 245, 251, 262, 273, 279, 290
century 4: 302, 313, 319, 330, 341, 347, 358, 369, 375, 386, 397
In the nowobsolete Julian calendar, the fourteen types of year (seven common, seven leap) repeat in a 28year cycle (1461 weeks). A leap year has two adjoining dominical letters (one for January and February and the other for March to December, as 29 February has no letter). This sequence occurs exactly once within a cycle, and every common letter thrice.
As the Julian calendar repeats after 28 years that means it will also repeat after 700 years, i.e. 25 cycles. The year's position in the cycle is given by the formula ((year + 8) mod 28) + 1). Years 2, 8 and 19 of the cycle are common years beginning on Wednesday. 2017 is year 10 of the cycle. Approximately 10.71% of all years are common years beginning on Wednesday.
Decade  1st  2nd  3rd  4th  5th  6th  7th  8th  9th  10th  

15th century  1410  —  1421  1427  1438  1449  1455  1466  1477  1483  1494  
16th century  1505  1511  1522  1533  1539  1550  —  1561  1567  1578  1589  1595  
17th century  1606  1617  1623  1634  1645  1651  1662  1673  1679  1690  —  
18th century  1701  1707  1718  1729  1735  1746  1757  1763  1774  1785  1791  
19th century  1802  1813  1819  1830  —  1841  1847  1858  1869  1875  1886  1897  
20th century  1903  1914  1925  1931  1942  1953  1959  1970  —  1981  1987  1998  
21st century  2009  2015  2026  2037  2043  2054  2065  2071  2082  2093  2099 
A common year starting on Sunday is any nonleap year that begins on Sunday, 1 January, and ends on Sunday, 31 December. Its dominical letter hence is A. The most recent year of such kind was 2017 and the next one will be 2023 in the Gregorian calendar, or, likewise, 2007, 2018 and 2029 in the obsolete Julian calendar, see below for more.
A common year starting on Friday is any nonleap year that begins on Friday, 1 January, and ends on Friday, 31 December. Its dominical letter hence is C. 2021, the current year, is a common year starting on a Friday in the Gregorian calendar. The last such year was 2010 and the next such year will be 2027 in the Gregorian calendar, or, likewise, 2005, 2011 and 2022 in the obsolete Julian calendar, see below for more. This common year is one of the three possible common years in which a century year can begin on, and occurs in century years that yield a remainder of 100 when divided by 400. The most recent such year was 1700 and the next one will be 2100.
A common year starting on Monday is any nonleap year that begins on Monday, 1 January, and ends on Monday, 31 December. Its dominical letter hence is G. The most recent year of such kind was 2018 and the next one will be 2029 in the Gregorian calendar, or likewise, 2013, 2019 and 2030 in the obsolete Julian calendar, see below for more. This common year is one of the three possible common years in which a century year can begin on and occurs in century years that yield a remainder of 300 when divided by 400. The most recent such year was 1900 and the next one will be 2300.
Dominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter depending on which day of the week the year starts on.
A leap year starting on Sunday is any year with 366 days that begins on Sunday, 1 January, and ends on Monday, 31 December. Its dominical letters hence are AG. The most recent year of such kind was 2012 and the next one will be 2040 in the Gregorian calendar or, likewise, 1996 and 2024 in the obsolete Julian calendar.
A common year starting on Tuesday is any nonleap year that begins on Tuesday, 1 January, and ends on Tuesday, 31 December. Its dominical letter hence is F. The most recent year of such kind was 2019 and the next one will be 2030, or, likewise, 2014 and 2025 in the obsolete Julian calendar, see below for more.
A leap year starting on Monday is any year with 366 days that begins on Monday, 1 January, and ends on Tuesday, 31 December. Its dominical letters hence are GF. The most recent year of such kind was 1996 and the next one will be 2024 in the Gregorian calendar or, likewise, 2008, and 2036 in the obsolete Julian calendar.
A leap year starting on Tuesday is any year with 366 days that begins on Tuesday, 1 January, and ends on Wednesday, 31 December. Its dominical letters hence are FE. The most recent year of such kind was 2008 and the next one will be 2036 in the Gregorian calendar or, likewise 2020 and 2048 in the obsolete Julian calendar.
A common year starting on Saturday is any nonleap year that begins on Saturday, 1 January, and ends on Saturday, 31 December. Its dominical letter hence is B. The most recent year of such kind was 2011 and the next one will be 2022 in the Gregorian calendar or, likewise, 2006, 2017 and 2023 in the obsolete Julian calendar. See below for more.
A common year starting on Thursday is any nonleap year that begins on Thursday, 1 January, and ends on Thursday, 31 December. Its dominical letter hence is D. The most recent year of such kind was 2015 and the next one will be 2026 in the Gregorian calendar or, likewise, 2010 and 2021 in the obsolete Julian calendar, see below for more.
A leap year starting on Saturday is any year with 366 days that begins on Saturday, 1 January, and ends on Sunday, 31 December. Its dominical letters hence are BA. The most recent year of such kind was 2000 and the next one will be 2028 in the Gregorian calendar or, likewise, 2012 and 2040 in the obsolescent Julian calendar. In the Gregorian calendar, years divisible by 400 are always leap years starting on Saturday. The most recent such year was 2000 and the next one will be 2400, see below for more.
A leap year starting on Friday is any year with 366 days that begins on Friday 1 January and ends on Saturday 31 December. Its dominical letters hence are CB. The most recent year of such kind was 2016 and the next one will be 2044 in the Gregorian calendar or, likewise, 2000 and 2028 in the obsolete Julian calendar.
A leap year starting on Thursday is any year with 366 days that begins on Thursday 1 January, and ends on Friday 31 December. Its dominical letters hence are DC. The most recent year of such kind was 2004 and the next one will be 2032 in the Gregorian calendar or, likewise, 2016 and 2044 in the obsolete Julian calendar.
A leap year starting on Wednesday is any year with 366 days that begins on Wednesday 1 January and ends on Thursday 31 December. Its dominical letters hence are ED. The most recent year of such kind was 2020 and the next one will be 2048, or likewise, 2004 and 2032 in the obsolete Julian calendar, see below for more.
The determination of the day of the week for any date may be performed with a variety of algorithms. In addition, perpetual calendars require no calculation by the user, and are essentially lookup tables. A typical application is to calculate the day of the week on which someone was born or a specific event occurred.
The Doomsday rule is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, drawing inspiration from Lewis Carroll's perpetual calendar algorithm. It takes advantage of each year having a certain day of the week upon which certain easytoremember dates, called the doomsdays, fall; for example, the last day of February, 4/4, 6/6, 8/8, 10/10, and 12/12 all occur on the same day of the week in any year. Applying the Doomsday algorithm involves three steps: Determination of the anchor day for the century, calculation of the anchor day for the year from the one for the century, and selection of the closest date out of those that always fall on the doomsday, e.g., 4/4 and 6/6, and count of the number of days between that date and the date in question to arrive at the day of the week. The technique applies to both the Gregorian calendar and the Julian calendar, although their doomsdays are usually different days of the week.
The solar cycle is a 28year cycle of the Julian calendar, and 400year cycle of the Gregorian calendar with respect to the week. It occurs because leap years occur every 4 years and there are 7 possible days to start a leap year, making a 28year sequence.
The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 and, before that, it was defined in ISO (R) 2015 since 1971. It is used (mainly) in government and business for fiscal years, as well as in timekeeping. This was previously known as "Industrial date coding". The system specifies a week year atop the Gregorian calendar by defining a notation for ordinal weeks of the year.
A century leap year is a leap year in the Gregorian calendar that is divisible by 400 without a remainder.
The Gregorian calendar is the calendar used in most of the world. It was introduced in October 1582 by Pope Gregory XIII as a minor modification of the Julian calendar, reducing the average year from 365.25 days to 365.2425 days, and adjusting for the drift in the 'tropical' or 'solar' year that the inaccuracy had caused during the intervening centuries.
Year starts  Common years  Leap years  

1 Jan  Count  Ratio  31 Dec  DL  DD  Count  Ratio  31 Dec  DL  DD  Count  Ratio  
Sun  58  14.50 %  Sun  A  Tue  43  10.75 %  Mon  AG  Wed  15  %  3.75
Sat  56  14.00 %  Sat  B  Mon  43  10.75 %  Sun  BA  Tue  13  %  3.25
Fri  58  14.50 %  Fri  C  Sun  43  10.75 %  Sat  CB  Mon  15  %  3.75
Thu  57  14.25 %  Thu  D  Sat  44  11.00 %  Fri  DC  Sun  13  %  3.25
Wed  57  14.25 %  Wed  E  Fri  43  10.75 %  Thu  ED  Sat  14  %  3.50
Tue  58  14.50 %  Tue  F  Thu  44  11.00 %  Wed  FE  Fri  14  %  3.50
Mon  56  14.00 %  Mon  G  Wed  43  10.75 %  Tue  GF  Thu  13  %  3.25
∑  400  100.0 %  303  75.75 %  97  24.25 % 