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The Luni-solar Modified Gregorian Calendar is a proposed new solar calendar that would replace the Gregorian calendar and solve some of its perceived problems that beg for calendar reform.

The Luni-solar Modified Gregorian Calendar is not necessarily an actual luni-solar calendar in that the months are not in sync with the moons cycles. But it does attempt to keep predictably out of sync by being out of sync only one day per month.

The new calendar does not change the number of days in a year or the number of months or the names of the months. It works simply by changing the number of days in most months, and moving leap day to the end of the year.

Month Length Quarter Length Equinox/Solstice
January 30 days 91 days March 19 or 20
February 31 days
March 30 days
April 31 days 92 days June 21
May 30 days
June 31 days
July 30 days 91 days September 22 or 23
August 31 days
September 30 days
October 31 days 91 (92) days December 21 or 22
November 30 days
December 30 (31) days

Leap Year[]

Leap day is added to the end of December, making December 31 days. December is the ideal place to add a day on leap year in this calendar because it's the only 30-day month that does not precede or follow a 31-day month, and because it's the last month of the year.

Leap years should happen every 4 or 5 years, not every 4 or 8 years as with the Gregorian calendar. So it is proposed that a better method be used for determining what years should be leap years than the current one.

The author of this calendar don't know what the best method is. I've heard that every 32 years an extra standard year should be inserted before the leap year making a 33 year cycle. But there might be even better solutions, so this definition of the calendar is left open.

Phasing in 5-Day Weeks[]

Some people think that the year should be shortened to 364 days so that it is evenly divisible by 7-the length of the week. But since the length of the week is whatever we make it, why not make the week 5 days long instead. Then the 365-day solar year would divide evenly into 73 weeks. And months would divide into 6 weeks.

Of course this would only work if there were no objections to changing the 7-day week to a 5-day week. But that is not going to happen unless the 5-day week is phased in slowly. People must be allowed to continue to observe 7-day weeks for an indefinite grace period while getting used to the idea. For religious reasons people should always be able to observe the 7-day Sabbath.

But maybe one day in the future if people would have everything they need, they wouldn't need to work more than 2 or 3 days a week, giving them the familiar 2 or 3 days off on the weekend. And then the 5-day week would be embraced.

If a 5-day week were to be established, the author of this calendar would suggest that the new days of the week be given new names unlike any of the current days of the week so as not to confuse them, and so that both 5- and 7-day weeks could be observed simultaneously.

If 5-day weeks were to be established, the author of this calendar would not use intercalary days. Ultimately he thinks it would be desirable to make leap day an intercalary day, but he would leave that as an option for future calendar reform.

Benefits of this calendar[]

  • The main benefit of this calendar is that the quarters are of similar lengths. One of the quarters is 1 day longer than the others but that is impossible to avoid without an intercalary day since the tropical solar year is 365 days and not evenly divisible by 4. But The author of this calendar decided not to use intercalary days because it doesn't make sense not to account for every day of the year. On leap years there are two quarters that are 1 day longer than the others.
  • All of the months are either 30 days or 31 days. There is no short month that is only 28 or 29 days to confuse everybody.
  • Any 2-month period will always be 60 or 61 days and most of them will be 61. That is not true on the Gregorian calendar where 2-month periods can be anywhere between 59 and 62 days.
  • The 31-day months always fall on even-numbered months and so are easier to remember.
  • Leap day is at the end of the year which is more intuitive and also does not change the number of days between January and February and the rest of the year like it does when leap day is in February.
  • Even though the months of this calendar are not in sync with the phases of the moon, the phases do repeat at the predictable interval of 1 month minus 1 day. That works because the lengths of the months alternate between 31 and 30 days creating a mean month length of 30.5 days, while the phases of the moon repeat on average every 29.53 days. December only has 30 days on standard years. But the interval is the same from January to December every year.
  • Equinoxes and solstices occur at about the same familiar time on this calendar as they would on the Gregorian calendar. That also means most dates line up with their corresponding dates on the Gregorian calendar, namely dates in the months April, June, and August through December. (For that to work, January 1 of this calendar would have to begin on Dec 31 Gregorian. Or you could skip a Gregorian leap year before starting this calendar. The point is you have to remove a day from the Gregorian year before you start this calendar.)
  • With 5-day weeks, this calendar could easily be turned into a perpetual calendar with only one intercalary day per leap year. That beats most other perpetual calendars that usually have at least 1 intercalary day per year if not more.


  • Most of the month lengths have been changed from their familiar lengths given to them by the Gregorian calendar.
  • 5 day weeks would be a big adjustment, even bigger than changing the number of days in each month. But 5-day weeks are not a requirement for this calendar. And as The author of this calendar said, both 5- and 7-day weeks could be observed simultaneously while people got used to the idea. So they could decide later to scrap it if it didn't catch on.

Similar Calendars[]

Daylight Saving Time and Time Zones[]

Most people don't like daylight saving time because it interferes with schedules and circadian rhythms. It's also different in different parts of the world, and even at opposite times of year in the Southern Hemisphere. The fact that the time changes at different places at different times makes it hard to keep track of time zone differences. It would just be easier not to have daylight saving time changes. On the other hand, most people like having a little extra daylight in the evenings. So the author of this calendar proposes to get rid of daylight saving time, and to redefine the time zones so that there is more light in the evenings year round in the redefined areas.

Some time zones are already defined this way, such as the province of Saskatchewan in Canada, and Iceland. They do not observe daylight saving time, yet they enjoy the benefit of having more daylight in the evenings because of the time zone that they have chosen to reside in. Solar noon in these areas is closer to 1 PM than 12 PM but that's the price that they pay and the author of this calendar doesn't think they are unhappier for it. There are drawbacks to doing this, mainly that morning commutes are made more difficult in the winter, especially in snow and ice. But not all areas would be affected by my proposal, and of the people who are affected, the ones with enough flexibliity would just go into work late in the winter.

Some things that the author of this calendar would do: The whole of the U.S. west coast would be become part of the Mountain time zone. For states like California, Nevada, Oregon, and Washington, this would mean being in UTC-7 year round instead of just 8 months of the year during daylight saving time. The Pacific time zone would not go away, since it would still be appropriate for use on the west coast of Canada (as it is now) and in Southeast Alaska (Juneau).

The author of this calendar would move the border of the Mountain, Central and Eastern time zones west. Mountain time would begin at the eastern border of Arizona (which is already a time-zone border 8 months of the year), continue through central Colorado, Wyoming and Montana along the Rockies, and then resume exactly where it is now along the west border of Saskatchewan.

Central time would begin at the eastern border of Texas, and continue north through the least populated areas of Arkansas, Missouri, Iowa, and Minnesota, and finally up the eastern border of Manitoba east of Winnipeg.

Eastern time would begin at the East Coast of Virginia, cut west of Maryland and Washington DC area, keep east of West Virginia and most of Virginia, cut through the center of Pennsylvania, stay west of New York, and continue north into Canada along the east border of Ontario. Everything east of that would be considered Atlantic time (UTC-4) except Newfoundland and Labrador which would become UTC-3.

In Europe, the author of this calendar would make the UK part of the UTC+1 time zone, and Sweden, Norway, Denmark, and central and eastern European countries part of UTC+2. The new time zone definitions would give more evening daylight to these regions making daylight saving time unnecessary.

Why not just keep the current time zone definitions and make daylight saving time year round? That would definitely be easier. But the problem is that some places would be too far west for their time zones. Places like Indianapolis that are at the western edge of their time zone already have daylight shifted to the evening (which is why until recently Indiana did not recognize daylight saving time). Daylight saving time year round in Indiana would shift too much daylight away from the morning. On the other hand, by redefining some places and not others, places like Pittsburgh that aren't very far west but don't get redefined wouldn't have any daylight shifted to the evenings at all. But The author of this calendar don't think that would be so bad.

None of this is set in stone. The general rule of thumb is to make sure that the timezones are such that the time of solar noon or the zenith of the sun always occurs after 12 PM rather than before, so that you always err on the side of daylight is in the evening when most people enjoy having more daylight.

Transitioning to the new time zones would happen the same way that Daylight Saving Time transitions, at 2 AM on the second Sunday of March, except that only affected areas would change their clocks, and the time change would be permanent.

Alternative to Daylight Saving Time[]

In addition to the proposals made above, the author of this calendar thinks that in the summers especially during the months of earliest sunrise: May, June, and July, that government offices and outdoor workers should be requested to start work earlier than usual. It would have the same effect that daylight saving time would have without the inconvenience of having to change clocks twice a year. It would also make working outside in the summer time easier by starting work earlier when it's cooler.