Calendar Reform, efforts to revise the calendar system to make up for defects in the Gregorian calendar. Calendar improvements have often been proposed to correct defects in the Gregorian calendar. Suggestions for official reform of the calendar have all failed, however, probably because people resist changing their traditional economic, religious, and social activities. Critics of the Gregorian calendar point out that it has 12 months of unequal length; no month is exactly one-twelfth of a year; the number of weeks in the quarter-year and half-year is uneven; and dates and days of the week vary from one year to the next.

One of the best-known proposals for calendar reform is the so-called World Calendar that was considered, but not adopted, in the United Nations in 1954. This calendar is based on a 52-week, 364-day year starting on Sunday, January 1, with the 365th day, called Year-End Day, intercalated, or added, without date or day of the week. In leap years an extra Leap-Year Day, also without date or day of the week, is inserted at the end of the 26th week, between the last day of June and the first day of July. The first month of each quarter has 31 days, and all the others have 30 days. The chief disadvantage of this calendar is that the Year-End Day interferes with regular religious observances.

The International Fixed Calendar (Thirteen-Month Calendar) is a proposal based on a year divided into 13 months of 28 days each, with the 365th day a Year Day, belonging to no week or month. In leap years an extra Leap Day is added after June 28. Half-years contain exactly 26 seven-day weeks and quarter-years exactly 13 weeks. All Sundays occur on the 1st, 8th, 15th, and 22nd of each month. The additional month, called Sol, is inserted as the seventh month between June and July. Although this calendar is uniform, it is criticized because national holidays would have to be changed.

A third fixed calendar, the Perpetual Calendar, has been proposed to the U.S. Congress without success. This calendar, like the World Calendar, has four 3-month quarters and adds an extra Year-End Day and Leap-Year Day. Monday is the first day of every week, and the quarters all begin on Monday, which is useful for business concerns.