Overview

A common year starting on Saturday is any non-leap year of 365 days in which January 1 falls on a Saturday. In traditional calendrical notation this arrangement corresponds to the dominical letter B. The weekday of January 1 fixes the weekday for every other fixed date in the year, so this single fact determines when recurring holidays and business cycles fall for the whole year.

Month beginnings and weekday mapping

Given January 1 on a Saturday in a common year, the first day of each month falls on the following weekdays (computed by adding the month lengths mod 7):

  • January 1: Saturday
  • February 1: Tuesday
  • March 1: Tuesday
  • April 1: Friday
  • May 1: Sunday
  • June 1: Wednesday
  • July 1: Friday
  • August 1: Monday
  • September 1: Thursday
  • October 1: Saturday
  • November 1: Tuesday
  • December 1: Thursday

From these starting weekdays one can derive the weekday of any date in the year by adding the day offset within a month mod 7. For example, December 25 falls on a Sunday in this configuration.

Friday the 13th and other date patterns

This common year type has exactly one Friday the 13th. With the month starts above, the 13th day of a month falls on Friday only in May (May 1 is Sunday, so May 13 is Friday). Knowing the start weekday for each month makes it straightforward to list which day of week any given date will have.

Holidays and common observances

When planning around widely observed fixed-date or weekday-based holidays, the start-of-year weekday determines their dates. In the U.S. pattern, for example: New Year’s Day is a Saturday; Martin Luther King Jr. Day (third Monday in January) falls on January 17; Valentine’s Day is Monday; Presidents Day (third Monday) is on February 21; Mother’s Day (second Sunday in May) is May 8; Memorial Day (last Monday in May) is May 30; Independence Day (July 4) is a Monday; Labor Day (first Monday in September) is September 5; Columbus Day is October 10; Halloween is Monday; Veterans Day is a Friday; Thanksgiving (fourth Thursday in November) is November 24; and Christmas is a Sunday. Movable observances such as Easter vary each year and are not fixed by the January 1 weekday.

ISO weeks and the year boundary

ISO week numbering (where weeks begin on Monday and week 1 contains January 4) interacts with this layout in a specific way. If January 1 is Saturday then January 1 and 2 fall in the last ISO week of the previous year. Whether that last week is numbered week 52 or week 53 depends on the previous calendar year: some previous-year configurations produce 53 ISO weeks while others produce 52. In practice this produces the occasional ambiguity when listing the ISO week number for the first weekend of January.

Gregorian and Julian occurrences

The same weekday arrangement can occur in both the Gregorian and Julian calendars, although the cycles that determine repetition differ. The Gregorian calendar repeats its full pattern every 400 years; the Julian calendar has a 28-year cycle for weekdays. Recent Gregorian examples of common years that began on Saturday include 1977, 1983, 1994, 2005, 2011, 2022 and 2033. In the Julian calendar counting, other years align similarly under that system; these examples illustrate how the theoretical pattern appears in practice.

Dominical letters and computation

The dominical letter is a historical aid that indicates which lettered day corresponds to Sunday for a given year. A common year uses a single dominical letter; for this configuration the letter is B. Modern calendar algorithms in software use arithmetic rules rather than dominical letters, but the letter system remains useful for some printed perpetual calendars and ecclesiastical computations.

Practical implications

Knowledge of the weekday layout helps with business planning, payroll schedules, school term timing, and event coordination. For example, when Christmas falls on a Sunday there are specific implications for retail hours, postal delivery schedules in some countries, and the allocation of observed public holidays that fall on weekends. The single Friday the 13th in May can be relevant for cultural or insurance-related work in sectors sensitive to that superstition.

This common-year type is one of three common years that contain only one Friday the 13th; the others are common years starting on Wednesday and common years starting on Friday. The same single-Friday-13th distribution also occurs in a leap year starting on Friday. Comparing these year types is helpful when studying patterns of holiday weekdays and the distribution of weekend days over a year.

Further reading and resources

For tables, technical notes and sample calendars consult the following links and example pages:

  1. Calendar overview and layout
  2. Definition of a common year
  3. Explanation of dominical letters
  4. Example: year 1977 calendar
  5. Example: year 1983 calendar
  6. Example: year 1994 calendar
  7. Example: year 2005 calendar
  8. Example: year 2011 calendar
  9. Example: year 2022 calendar
  10. Example: year 2033 calendar
  11. Notes on the Gregorian calendar
  12. Notes on the Julian calendar
  13. Julian example: year 2017
  14. Julian example: year 2023
  15. Related: common year starting on Wednesday
  16. Related: common year starting on Friday
  17. Related: leap year starting on Friday
  18. Definition and rules for leap years