A common year starting on Monday is any non-leap year (i.e., a year with 365 days) 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. The century year, 1900, was also a common year starting on Monday in the Gregorian calendar. See below for more. Any common year that starts on Sunday, Monday or Tuesday has two Friday the 13ths. This common year of this type contains two Friday the 13ths in April and July. Leap years starting on Sunday share this characteristic, but also have another in January.
Calendar for any common year starting on Monday,
In the (currently used) Gregorian calendar, along with Sunday, Wednesday, Friday or Saturday, the fourteen types of year (seven common, seven leap) repeat in a 400-year cycle (20871 weeks). Forty-three common years per cycle or exactly 10.75% start on a Monday. The 28-year sub-cycle does only span across century years divisible by 400, e.g. 1600, 2000, and 2400.
|16th century||prior to first adoption (proleptic)||1590||--|
In the now-obsolete Julian calendar, the fourteen types of year (seven common, seven leap) repeat in a 28-year 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 6, 12 and 23 of the cycle are common years beginning on Monday. 2017 is year 10 of the cycle. Approximately 10.71% of all years are common years beginning on Monday.
|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 %|