Common year starting on Thursday


A common year starting on Thursday is any non-leap 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]. This common year contains the most Friday the 13ths; specifically, the months of February, March, and November. Leap years starting on Sunday share this characteristic.
From February until March in this type of year is also the shortest period that occurs within a Friday the 13th. In 1998, for example, February 13th, March 13th and November 13th, all occurred on a Friday, so there were 3 Friday the 13ths in 1998, February, March and November.

Calendars

Applicable years

Gregorian Calendar

In the Gregorian calendar, alongside Tuesday, the fourteen types of year repeat in a 400-year cycle. Forty-four common years per cycle or exactly 11% start on a Thursday. The 28-year sub-cycle does only span across century years divisible by 400, e.g. 1600, 2000, and 2400.

Julian Calendar

In the now-obsolete Julian calendar, the fourteen types of year repeat in a 28-year cycle. A leap year has two adjoining dominical letters. 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 + 1). Years 3, 14 and 20 of the cycle are common years beginning on Thursday. 2017 is year 10 of the cycle. Approximately 10.71% of all years are common years beginning on Thursday.