The Symmetry454 Calendar (Sym454) is a proposal for calendar reform proposed by Dr. Irv Bromberg of the University of Toronto. It is a perpetual solar calendar that conserves the traditional 7-day week, has symmetrical equal quarters, and starts every month on Monday.

The proposed calendar is laid out as follows. The last seven days of December are intercalary days and do not occur every year.

The calendar is called Symmetry 454 because each quarter has 3 months composed of 4 + 5 + 4 weeks (91 days). Evenly-balanced quarters are desireable for businesses because they aid in fiscal planning. The only exception to the 91-day quarters are the last quarter of leap years, which have an extra intercalary week.

All months have a whole number of weeks, so no month ever has a partial week.

There are no "null" days -- alignment of the weekday cycle with New Year Day is accomplished by using a Leap Week instead. In leap years, which occur every 5 or 6 years, December becomes a 5-week month. The leap week is shown in bold in the above calendar.

All holidays, birthdays, anniversaries, etc. are permanently fixed. The ordinal day number and ordinal week number of every Symmetry454 date is permanently fixed.

The "Kalendis" calendar calculator demonstrates the Symmetry454 calendar and interconverts dates between it (Symmetry454) and other calendars.

The Symmetry454 arithmetic is fully documented and placed in the public domain for computer implementation.

Easter on a fixed date

The World Council of Churches (WCC) Easter web page indicates that the WCC is interested in:

• a perpetual calendar that preserves the traditional 7-day sabbatical cycle
• the calendar must not employ any "null" days that are outside of the normal 7-day week
• the calendar may have a fixed date for Easter, but it must be permanently on a true Sunday and the choice of date must be justifiable
• ideally the calendar should permanently maintain alignment with the solar cycle

The Symmetry454 Calendar meets all of the WCC criteria.

External links

The Symmetry454 Calendar and the Kalendis Calendar Calculator

SymISO, a converter for dates between the Gregorian, Symmetry454 and ISO calendars.