page_title: Hanke–Henry Permanent Calendar
section_title: History
hierarchical_section_title: Hanke–Henry Permanent Calendar / History
caption_attribution_description: English: Steve Hanke-Richard Henry Permanent Calendar Squeakycatta (talk) 07:52, 1 January 2012 (UTC)
context_page_description: The Hanke–Henry Permanent Calendar is a proposal for calendar reform. It is one of many examples of leap week calendars, calendars which maintain synchronization with the solar year by intercalating entire weeks rather than single days. It is a modification of a previous proposal, Common-Civil-Calendar-and-Time. With the Hanke–Henry Permanent Calendar, every calendar date always falls on the same day of the week.
context_section_description: In 2004, Richard Conn Henry, a professor of astronomy at Johns Hopkins University, proposed the adoption of a calendar known as Common-Civil-Calendar-and-Time (CCC&T), which he described as a modification to a proposal by Robert McClenon. Henry's original version had essentially the same structure given above, but inserted its leap week named "Newton" between June and July in the middle of the year. 
  The leap rule was chosen to match the ISO week leap rule, to minimise the variation in the start of the year relative to the Gregorian calendar, whereas Robert McClenon originally proposed a simple leap rule which would result in larger astronomic variance: Years whose numbers are divisible by 5 had a leap week, but years whose numbers are divisible by 40 did not unless they are also divisible by 400.
  Henry had advocated transition to the calendar on 1 January 2006 as that is a year in which his calendar and the Gregorian calendar begin the year on the same day. After that date passed, he recommended dropping off 31 December 2006 to start in 2007, or dropping 30 and 31 December 2007 to start 2008.
  In late 2011 the calendar was revised by Johns Hopkins economist Steve Hanke by moving the leap week from the middle to the end of the year and renaming it "Extra", producing the Hanke–Henry Permanent Calendar. The target date for universal adoption was 1 January 2017 then, but has been postponed to 2018, when the calendar design was changed in early 2016 to adopt Monday as the start of the week, quarter and year, to better comply with existing international standard ISO 8601.
  In 2016, web developer Black Tent Digital released the official Hanke-Henry calendar app, with capabilities to convert between Gregorian and Hanke-Henry Calendars, in order to facilitate transition to the Hanke-Henry system. It is no longer available as of March, 2018.
caption: Hanke–Henry Permanent Calendar pre-2016 version with weeks still starting Sunday, but Xtra already at the end of the year
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