The New Celtic Calendar

Today’s date in the New Celtic Calendar is: 16 Eilmì, 3048

The New Celtic Calendar is a notional and experimental calendar devised by the author purely for personal interest. It is not meant to represent any real calendar that may or may not have ever existed at any time, nor is it a suggestion for calendar reform.

I have been fascinated by calendars, and particularly lunisolar ones, for some time, and after reading about the Coligny Calendar I was inspired to try and create a lunisolar calendar that was as accurate as possible but using relatively simple rules.

Mean Months and Years

Whilst the Coligny Calendar apparently used a 5-year cycle, possibly repeating over a longer cycle of 30 years, I chose to use the 19-year Metonic Cycle, which is more accurate. This cycle is used to determine the years in which an extra month, the Intercalary Month, is added in order to keep the calendar in tune with the solar year. Other adjustments need to be made over longer periods of time to keep the calendar in sync with the lunar cycles as well as the solar year. The aim, to be specific, is to achieve a mean lunar month as close to the actual mean synodic month (the time it takes for the moon to move from a particular phase to the next time it is at that same phase, e.g. from new moon to new moon) and a mean year as close to the actual mean solar year as possible.

A “standard” lunar year has 12 months alternating between 29 or 30 days long, and can have a total of 354 or 355 days depending on the sequence of months. This is 10 or 11 days short of a normal solar year, so unless additional “intercalary” months are added, the calendar will become out of synchronisation with the solar year, and the months will fall at the wrong time of year. To keep the year in synchronisation a system of 19-year cycles, called “Metonic cycles”, is used and 7 years out of these 19 (years 2, 5, 7, 10, 13, 16 and 18) have an extra month added at the end of the year. (Interestingly, these are one year before the equivalent years in the Hebrew calendar’s 19-year cycle.) These 13-month years are called Long Years, and as the additional month can have 29 or 30 days, a Long Year can have between 383 and 385 days.

To keep the calendar aligned on a long-term basis, 8 years are omitted from every 19th cycle, so there is a “Grand Cycle” of 18 cycles of 19 years and one of 11 years. In the 11-year cycle only 4 years are Long Years (years 2, 5, 7 and 10). This system produces a mean year length of 365.242333363935245 days, which is very close to the actual mean solar year length. The short cycle occurs in the 10th cycle of every 19, i.e. in the mid-point of the Grand Cycle (when MOD 19 = 10).

To keep accuracy with the lunar cycle, I have chosen to use the ready-made Yerm Lunar Calendar, devised by Karl Palmen, which alternates 29- and 30-day months according to a simple rule-based cycle. I chose this system as it is the most accurate system, not being tied to the solar year, thus allowing the cycle to accurately follow the lunar cycles and without complicated rules.

Using this system, months alternate between 30-day and 29-days, but periodically there are two 30-day months in a row. However there are never two 29-day months in a row. The cycle operates over a period of 52 “Yerms”, each of which can have either 15 or 17 months, and which start and finish with a 30-day month. Using this system produces a mean lunar month of 29.530588 days, which is very close to the actual mean lunar month in the current era. This of course may need to be adjusted in the long term to keep pace with changes in the length of a lunar month but it suffices for us in our present era.

So, the calendar uses the Metonic cycle with an extra month added in certain years to keep it in sync with the solar year, and the Yerm Lunar Calendar to determine the start and end dates of each month, and therefore the length of each month.

Structure of the Months

I decided to make this a “Celtic” calendar as inspired by the Coligny Calendar, except that I have applied “Gaelicised” versions of the Gaulish names. These names are pure conjecture, and represent an imaginary morphing of the names from the Gaulish ones over time if they had been used in Scotland. For example Cadal in modern Scots Gaelic means “to sleep” or “sleeping”, but the name has been chosen as a possible corruption of the Gaulish Kantlos. The names are the ones suggested by “Ray White” on his now defunct web site at and should not be taken as scholarly conclusions as to what these names would have been.

The months in the calendar are as follows:

Moon Pronunciation Meaning
Samhain Sa-win (Summer’s End/Seeding?)
Dumhainn Doo-win (World Darkness/Silence?)
Riùr Roor (Cold & Ice/Royal Burning?)
Naghaid Nagh-hidge (Staying at Home/House of the Eaten One?)
Uarain Oo-urr-in (Cold/Cold’s End/Keenly Runs?)
Cuithe Koo-ee-huh (Wind/House of the Hound?)
Geamhain Ghee-ow-in (Winter’s End/Sprouting?)
Siùfainn Shoo-fin (Half-spring/Brightening?)
Eacha Ech-uh (Horse/Dampening?)
Eilmì Ail-mee (Claim/Evocation of the Stag?)
Aodhrain Urr-in (Arbitration/Causes to Run?)
Cadal Cad-ull (Song/Tail of the Dog?)
Eadràn * Aid-rahn (Intercalary/Between?)
* Is added in years 2, 5, 7, 10, 13, 16 and 18 of every cycle, apart from the 10th out of every 19 cycles, when a month is added in years 2, 5, 7 and 10.
Start of the Year

There is much debate about the names of the months and when the year should start. In fact it is not known even if the months occurred at the times of the year depicted in this calendar, for example “Samonios” may not be cognate with “Samhain”, and some scholars suggest that it may have actually occurred around the time of Beltane in April/May. However, I have chosen to start the calendar at around the time of Samhain, i.e. October-November, for a couple of reasons.

The first reason is that when I first came across the Gaulish Calendar, it seemed to be the consensus that Samoni was cognate with Samhain, and I proceeded on that basis. The second is a more personal reason, as the date of 9th November is significant to me and this is one of the reasons I have chosen this date to begin each lunar cycle, or thereabouts as the dates pan out.

The articles I have read propounding that the calendar should start at around the time of Beltane are very compelling and I could rearrange everything accordingly. However, I have use this calendar under the current methodology for around 15 or more years now, and have got used to the months taking place when they do, and to change it all now would be very jarring. So, the dates, cycles, months etc shall all remain as they are and, suffice it to say choosing to start a Celtic Calendar at Samhain, whether or not this is actually connected with the Gaulish Calendar in any way, doesn’t seem to be an entirely unlikely concept.

Epoch and New Year Dates

The epoch (i.e. the date of the first day of the calendar) is 8th November -1026 Gregorian (i.e. 1,027 B.C.E.). This date was not chosen specifically but was arrived at by working back from the start date of the current cycle at the time of devising, i.e. 9th November 1999. The latter date was chosen partly for personal reasons, but also it means that with the structure of the 19-year cycle that I am using, the “mean new year” occurs, as far as possible, at Lunar Samhain, that is to say, at or near the New Moon in the astrological sign of Scorpio. This means that the “mean new year” date is the 7th November, which is roughly when the sun is at 15˚ Scorpio, the mid-point between the autumnal equinox and the winter solstice in the northern hemisphere. Within a 19-year cycle, the date of the start of each year thus varies from around 23rd October to 21st November.

Some traditions would place the new year date, i.e. the start of the month of Samhain, earlier than this so that it is the full moon that is closest to the midpoint that Samhain is celebrated. In my version, however, Samhain is celebrated at the nearest new moon, when fires were lit to lighten what was considered the darkest night of the year, when the veil between this world and the next was at its thinnest. This ritual may have similar origins to Diwali, the Hindi festival of lights, which coincides with the Celtic new year in my calendar in most years. This Lunar Samhain is also sometimes called The Witch’s New Year in Wiccan and other practices.

The following table shows the starting dates of each year in the current trio of lunar cycles.

Cycle 163
Cycle 164
Cycle 165
8 Nov, 1980
9 Nov, 1999
8 Nov, 2018
28 Oct, 1981
28 Oct, 2000
29 Oct, 2019
16 Nov, 1982
16 Nov, 2001
16 Nov, 2020
6 Nov, 1983
5 Nov, 2002
5 Nov, 2021
25 Oct, 1984
26 Oct, 2003
25 Oct, 2022
13 Nov, 1985
13 Nov, 2004
13 Nov, 2023
2 Nov, 1986
2 Nov, 2005
2 Nov, 2024
21 Nov, 1987
21 Nov, 2006
20 Nov, 2025
9 Nov, 1988
10 Nov, 2007
10 Nov, 2026
30 Oct, 1989
30 Oct, 2008
30 Oct, 2027
18 Nov, 1990
17 Nov, 2009
17 Nov, 2028
7 Nov, 1991
7 Nov, 2010
6 Nov, 2029
26 Oct, 1992
27 Oct, 2011
27 Oct, 2030
14 Nov, 1993
14 Nov, 2012
15 Nov, 2031
4 Nov, 1994
3 Nov, 2013
3 Nov, 2032
24 Oct, 1995
24 Oct, 2014
23 Oct, 2033
11 Nov, 1996
12 Nov, 2015
11 Nov, 2034
31 Oct, 1997
31 Oct, 2016
1 Nov, 2035
19 Nov, 1998
19 Nov, 2017
19 Nov, 2036
Date Conversion

The following tools can be used to convert dates in the Gregorian calendar to those in the New Celtic Calendar and create printable calendars for the current Celtic month and for months in the past and future.