The Anglo-Saxon Calendar

This is a purely notional calendar that I have invented, based upon various known aspects of solar calendars in the past and traditions in England, many of which still survive today. This page explains how the calendar is structured. It is not intended to be a proposal for calendar reform, which I have detailed elsewhere, but just for my personal interest.

How it works

The ancient Anglo-Saxon calendar was reputed to be a luni-solar calendar, following the cycles of the moon with an extra month added every few years to keep it in line with the seasons. This calendar was reputed to have its new year on Christmas Eve, but this would not be possible every year if the calendar were luni-solar, due to the lunar year not matching the solar year. There is speculation that the 12 days of Christmas may have been epagomenal days added at the end of the year to compensate for this but this is speculative and would have brought most years up to 366 days in length. which is too long.

The calendar I have devised, however, is a solar one using Anglo-Saxon month names, in the same vein as Tolkien's Shire calendar. It is purely solar, with either 365 or 366 days depending on whether the year is common or leap, and the year starts on the date of the northern winter solstice (in this article this is called the south solstice as it is when the sun reaches its most southerly latitude). The months are arranged primarily so that each season starts on the first of the appropriate month, e.g. spring begins on the first day of Eostremonath. This does not always happen for every season every year, but the most important characteristics are that the first day of the year should always fall on the date of the northern winter solstice and that the first day of Eostremonath should, as far as is possible, fall on the date of the northern spring equinox (northward equinox). The latter is to ensure that the Egg Moon, the first full moon of spring, falls in the month of Eostremonath. So under this system winter has 89 days, spring has 93 days, summer has 93 or 94 days and autumn has 90 days.

The following table shows the months with their lengths and their usual start dates in the Gregorian calendar. These dates can vary by a day or so either side of the given dates due to the different cycles of leap years between the two calendars. Leap years in the calendar depend on the number of days between each winter solstice, and in those years where there are 366 days between these days, an extra day is added to the summer month of Weodmonath, making it 32 days long. Therefore there is no simple arithmetic leap rule in this calendar.



Usual starting dates


21 December
20 January
18 February
20 March
20 April
21 May
21 June
22 July
31 {32}
22 August
22 September
22 October
21 November


The epoch for the calendar is the year 444 C.E. and the era is called A.S.E. (Anglo-Saxon Era). The years are therefore approximately 444 years behind those of the Gregorian calendar.

Days of the week

The days of the week were named after Norse deities, apart from Saturday, Sunday and Monday, and have the same origins as the names that are still used today. The Old English names for the days of the week were: Sunnandæg, Monandæg, Tiwesdæg, Wodnesdæg, Þunresdæg, Frigedæg, and Sæternesdæg.


The main festive days observed in the calendar are as follows, with typical equivalent dates in the Gregorian calendar:

  • Yule, 30 Aergiuli - 1 Aeftergiuli (20th - 21st December)
  • Winter Cross Quarter, 16 Solmonath (4th February)
  • Ostara, 1 Eostremonath (21st March)
  • Egg Moon (Movable - first full moon of spring)
  • Spring Cross Quarter, 16 Thrimilchi (5th May)
  • Litha, 31 Aerlitha - 1 Aefterlitha (21st - 22nd June)
  • Summer Cross Quarter, 16 Weodmonath (6th August)
  • Harvest Moon (Movable - last full moon of summer)
  • Mabon/Harvest Home, 31 Halegmonath (21st September)
  • Autumn Cross Quarter, 16 Blotmonath (6th November)

In popular parlance, the Harvest Moon is the full moon closest to the autumnal equinox, therefore it could occur in the last half of Holimonth or the first half of Winterfylleth. In more northern climes, however, harvest would tend to occur earlier than this, and this fits with it being the last full moon before the equinox in my calendar. This means that it will usually fall in the month of Holimonth, which interestingly enough, has the alternative name of "Harvestmonth" (Haerfestmonath).

More on leap years

The rule for leaps years is simple - if there are 366 days between one winter solstice and the next, then the year is a leap year. If we wish to autamte this for representation on a computer system, we must have some way of calculating when each winter solstice will occur in GMT. There are arithmetical formulae to work this out, but they are very complex. However, to reduce this complexity we can use a variable, or progressive, rule, rather than a fixed one. In the case of the south solstitial year, i.e. the year between two south solstices, this was relatively stable up to around 1500 CE, is currently getting shorter at a relatively high rate, and will stabilise again around 9000 CE. The rule employed therefore uses a linear approximation of the downward curve of the mean south solstitial year length during this period. It is not as simple as a fixed rule, but is simpler than the astronomical algorithm required to do the same thing.

The rule employed is called LASSY, which stands for Linear Approximation to the South Solstitial Year, and was devised by Dr. Irv Bromberg of the University of Toronto. Dr. Bromberg has devised several leap rules for use with experimental or notional calendars, in particular his Symmetry454 calendar, a calendar that uses a "leap week" instead of a leap day to keep it in synchronisation with the seasons. I have used his freely available algorithm to work out the start dates for my calendar for the A-S years 1 to 2556 (i.e. 444 to 3000 CE), with the offset parameter adjusted to -11.2, which appears to give the closest approximation to the date of the south solstice. I have checked as many of the resultant start dates against approximated solstice dates and so far only one year is out of sync, and on that occasion it is estimated that the solstice will occur one minute into the following day, so the rule is so far proving to be pretty accurate.

For more information on this subject, see the links below. I am extremely indebted to Dr. Bromberg for the information and the algorithms that he has made freely available on his web site, which have enabled me to employ this leap rule to my calendar. The graphs and diagrams are worth a look in order to gain an appreciation of how the orbital mechanics of the Earth work, and how these factors must be taken into account when devising a calendar.