Hanke-Henry Permanent Calendar

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Hanke-Henry Permanent Calendar is a proposed new calendar which aims to reform the current Gregorian Calendar by making every year identical. With the Hanke-Henry Permanent Calendar, every calendar date always falls on the same day of the week.

Hanke-Henry Permanent Calendar Proposal

Correcting for drift[edit]

While many calendar reforms aim to make the calendar more accurate, the Hanke-Henry Permanent Calendar focuses on making the calendar perennial, so that every date falls on the same day of the week, year after year.[1] The familiar drift of weekdays with respect to dates results from the fact that the number of days in a physical year (one full orbit of earth around the sun, approximately 365.24 days) is not a multiple of seven. By reducing common years to 364 days (52 weeks), and adding an extra week every five or six years, The Hanke-Henry Permanent Calendar eliminates weekday drift and synchronizes the calendar year with the seasonal change as the Earth circles the Sun. The extra week, or "mini-month", known as "Xtr (or Extra)",[1] would occur every year that either begins or ends in a Thursday on the corresponding Gregorian calendar.[1] The extra week would fall between the end of December and the beginning of January.

Under the Hanke-Henry Permanent Calendar there are two 30 day months followed by one month of 31 days. While the Hanke-Henry Permanent Calendar changes the length of the months, the week and days remain the same.[2]


  • Holidays such as Christmas and New Year's Day as well as birthdays always occur on the same day of the week every year.
  • The calendar itself is permanent, it does not change year to year, with the exception of the need to add a week at the end of every 5 or 6 years.
  • Quarters all have the same number of days simplifying financial calculations. This calendar would also have prevented Apple’s Q4 2012 reporting fiasco. [3]
  • Unlike many other reform proposals, it does not change the days of the week.
  • The calendar starts on the same day every year, Sunday, the 1st of January.
  • As in the Gregorian calendar, Sunday to Sunday is always seven days, as is Saturday to Saturday, or Friday to Friday. Because no days are ever added outside a seven-day week, there should be no objection from religious groups concerned about weekly holy days. (In proposals that add single days outside the week, a true "seventh day" of rest or worship would drift between weekends and weekdays.)


  • Not as precisely aligned with the solar year as the existing Gregorian calendar and some proposed reform calendars.
  • Requires continued use of the Gregorian calendar for certain agricultural purposes.
  • All computer date-handling will have to be fixed, which will be much more complicated than the Y2K fix.
  • US-biased, not compatible with international standards, such as ISO 8601, which start the week on Monday, hence also the week year. This issue could be resolved by modifying the calendar to begin in a year where 1 January falls on a Monday, instead of a Sunday. e.g. Monday, 1 January 2018 instead of Sunday, 1 January 2012.
  • There is no 31st of October, removing Halloween from the current date.

Other calendar reform proposals[edit]

  • Leap week calendar Week added at the end of certain years.
  • The World Calendar A 12-month, perennial calendar with equal quarters proposed by Elisabeth Achelis in the 1930s.
  • International Fixed Calendar A perennial calendar with 13 months of 28 days each, with one day at the end of each year belonging to no month or week. It is also known as the Cotsworth plan and the Eastman plan.


  1. ^ a b c "The Hanke-Henry Date and Time, Everywhere in the World"
  2. ^ "Is It Time to Overhaul the Calendar?", by Stephanie Pappas, Scientific American.
  3. ^ [1], GlobeAsia, 2013

External links[edit]