A Runic calendar (also Rune staff or Runic Almanac) is a perpetual calendar based on the 19-year-
long Metonic cycle of the Moon. Runic calendars were written on parchment or carved onto staves of wood, bone, or horn. The oldest one known, and the only one from the Middle Ages, is the Nyköping staff from Sweden, believed to date from the 13th century. Most of the several thousand which survive are wooden calendars dating from the 16th and the 17th centuries. During the 18th century, the Runic calendars had a renaissance, and around 1800, such calendars were made in the form of tobacco boxes in brass.

A typical Runic calendar consisted of several horizontal lines of symbols, one above the other.

Special days like solstices, equinoxes, and celebrations (including Christian holidays and feasts) were marked with additional lines of symbols.

The calendar does not rely on knowledge of the length of the tropical year or of the occurrence of leap years. It is set at the beginning of each year by observing the first full moon after the winter solstice. The first full moon also marked the date of Disting, a pagan feast and a fair day.

A primstav (translation: prime staff) is the ancient Norwegian calendar stick. These were engraved with images instead of runes. The images depicted the different nonmoving religious holidays. The oldest primstav still in existence is from 1457 and is exhibited at Norsk Folkemuseum.

The Icelandic calendar developed in the 10th century, which inspired by the Julian calendar introduced a purely solar reckoning, with a year having a fixed number of weeks (52 weeks or 364 days). This necessitated the introduction of "leap weeks" instead of the Julian leap days.
The old Icelandic calendar is not in official use any more, but some Icelandic holidays and annual feasts are still calculated from it. It has 12 months, broken down into two groups of six often termed "winter months" and "summer months". The calendar is peculiar in that the months always start on the same day of week rather than on the same date. Hence Þorri always started on a Friday sometime between 9 and 15 January of the Julian calendar, Góa always starts on a Sunday between 8 and 14 February of the Julian calendar.
  • Skammdegi ("Short days")
  1. Gormánuður (mid October – mid November, "slaughter month" or "Gór's month")
  2. Ýlir (mid November – mid December, "Yule month")
  3. Mörsugur (mid December – mid January, "fat sucking month")
  4. Þorri (mid January – mid February, "frozen snow month")
  5. Góa (mid February – mid March, "Góa's month", see Nór)
  6. Einmánuður (mid March – mid April, "lone" or "single month")
  • Náttleysi ("Nightless days")
  1. Harpa (mid April – mid May) Harpa is a female name, probably a forgotten goddess. The first day of Harpa is celebrated as Sumardagurinn fyrsti, the First Day of Summer
  2. Skerpla (mid May – mid June, another forgotten goddess)
  3. Sólmánuður (mid June – mid July, "sun month")
  4. Heyannir (mid July – mid August, "hay business month")
  5. Tvímánuður (mid August – mid September, "two" or "second month")
  6. Haustmánuður (mid September – mid October, "autumn month")

At what times did the Norsemen hold their blót feasts, their blótveizla?
Let’s start with Yule. Contrary to popular belief, the mid-winter blot has has very little to do with the winter solstice. Actually it takes place almost a month later. Whatever was celebrated, if anything at all on the solstice, it was neither Yule, nor mid winter. To find out this all you have to do is have a look at the Norse and Icelandic calendars, as well as the other Germanic calendar we have knowledge of. In addition we have the Norwegian Prime staffs and their cousins in Sweden, as well as source material in the sagas to go on.
Lets slook at  the Norse calendar. The Norsemen divided the year into two equal parts. Summer and winter. These were called skammdegi – winter and nóttleysa – summer. We know that skammdegi started with vetrnætr – winter nights. In Norway this time was set to the time around the 14th of October. In Iceland about a week later as they used a different method of reckoning when the holy days was.
Likewise nóttleysa started on the 14th of April with sumarmål the first day of summer in Norway. Since we know when the first day of winter and the first day of summer was, mid-winter must be in the middle of these two days. That brings us to mid january. In Haakon the Goods saga in Heimkringla, it clearly says:
“King Haakon was a good and Christian man  when he arrived in Norway. But the country was heathen, and there where many blót and many great men, and he needed the help and friendship of the people, and he let it be secret that he was christian, but held Sunday and Friday fast. He made it law that Yule should start at the same time as with christian people, every man should make beer from one “mål” of malt or pay fines, and the holidays last as long as there where beer left.
Before this, they started Yule on hökunótt, that was midwinter night
(12. january), and then they held Yule for 3 nights.”
Sandal of writes: “The Nordic mid-winter was from then on timed to the last day of Christmas (20th day christmas, 13th of January). This day like the the 13th day is in according to old folk traditions called “old yule day”. In Sogn og Fjordane county mid-winter on the 12th of January is said to be old  new years day. This is because in the older christian tradition, Christmas also marked the beginning of the new year.”
If that is not enough we have Orkneyinga saga confirming this. It tells of King Thorri,
Thorri was a great blótsman, every year in the middle of winter he held what they called Thorri blót, and from that the month received its name.
Since we know that Thorri starts in mid-january, according to Norwegian fixed tradition on the 13th of January we know that mid winter, and therefore Thorri’s blot must have been around this time. Thorri blot is still a strong tradition in Iceland as a feast after it was reintroduced in the national romantic era of the 19th century.
The next great blót of the year was the spring blot. Again we start by looking at the norse calendar. Since each half of the year was six months, to find the time of the spring blot, all we have to do is divide the six months between hökunótt and mid summer. Of course mid summer here is not the summer solstice. But old mid summer, and that was according to the set dates of the Norwegian prime staff, and old folk customs on the 14th of July. That will place the blót held in spring firmly around the 14th of April. This is also the day that we turn the prime staff so that the summer side is facing up, and is the traditional first day of summer in Norway, also called “sommermål” from the old Norse – sumarmál.
This also coincide with the old German calendar, that places the Sumarmál in the middle of Ostermond. The blót at Sumarmál was also called Sigrblót. The Blótveizla was made in honor of Odin, for victory in war. Summer was a dangerous time, when the leiðangr may be called to defend the land, or expeditions of war be mounted. But that was likely the grand public ceremonies lead by the king, the jarls and other great men. For the farmer it was time for the várblot. Probably in the honor of Frey.
With mid-winter in the middle of January, the summer solstice is of course not the time for the mid-summer blot. On the prime staff we find, according to old Norwegian tradition a mark in the middle between Sumarmál and vetrnætr. The day is the 14th of july. We also find this day on the German calendar as altes mittsommer. But there is no evidence that there was a great blótveizla in the summer. In the story of Asbjørn Selsbane in the Saga of Olav Haraldsson, Snorri writes:
As long as heathenism prevailed, Sigurd usually had three sacrifices every year: one on winter-night’s eve, one on mid-winter’s eve, and the third towards summer.
The lack of a dedicated public blótveizla in the summer can be explained. The summer was a busy time. Trade and war expeditions where mounted, the farmers where busy securing their harvest. But there was also another function of society that took place in the summer. The Allþing. So any huge religious celebration may have coincided with or been a part of the þing at this time of the year.
The final great blót of the year took place in the middle of October. Snorri places the day at winter-nights – vetrnætr in the Story of Asbjørn Selsbane. And again from Nordic tradition this was the first day, or rather night of winter. In Heimskringla we find several references to this:
-In autumn the news was brought to King Olaf that the bondes had a great feast on the first winter-day’s eve, at which there was a numerous attendance and much drinking; and it was told the king that all the remembrance-cups to the Asas, or old gods, were blessed according to the old heathen forms; and it was added, that cattle and horses had been slain, and the altars sprinkled with their blood, and the sacrifices accompanied with the prayer that was made to obtain good seasons. It was also reported that all men saw clearly that the gods were offended at the Halogaland people turning Christian.
The first day of winter, according to the primestaff, Worms Norwegian runic calendar, the Gudbrandsdal runic calendar, etc, falls on the 13th of October. This is the start of winter nights – vetrnætr. In Viga-Glum’s Saga it says that dísablót was held around this time. That they offered prayers for a good season corresponds well with what is told about the vetrnætr in Viga-Glum’s Saga.
– A feast was held at the beginning of Winter, and sacrifice made to the disir, and everyone had to take part in this observance.
The disir was connected with Frey, so the prayer to obtain good seasons was likely to be the old formula til árs ok friðar – for a good year and peace.  Ár translates of course to “year” but it can also be “åring” ,and that is a word that means “crop”.  just as haust still means both harvest time and crops. The Icelanders are still saying «óskum öllum (we wish all) árs og friðar» – a good year and peace.
Now to confuse matters a bit. In Iceland and probably elsewhere, they did not operate with exactly the same times as in Norway. Climatic differences may be the reason for this. But here is a short recepee for how the Icelanders reckoned at what times the three great public blót was to be held. They started with the winter solstice and according to icelandic tradition hökunótt was always on a Friday between the 19th and 25th of january, while the first summer day always starts on a Tuesday between the 19th and 25th of April, and vetrnætr is always in the 26th week of summer, on a saturday between the 19th and 26th of october.
In his book Jul, disting och förkyrklig tideräkning – 2006 (ISBN ISBN 91-85352-62-4), Andreas Nordberg says that hökunótt was always 28 days or 4 full weeks,  after the winter solstice. And likewise somarmál was 28 days after the spring equinox, mid- summer was 28 after the summer solstice and vetrnætr 28 days after the autumn equinox.
Another tradition is that Yule was to be celebrated at the full moon in the yule month. And the yule month started on the first new moon after the solstice. In other words. Yule is to be celebrated on the first full moon after the first new moon, after the solstice.
I think we can safely assume that these three blótveizla was not celebrated on the solstices like modern neo-pagans, wiccans and many Asutru and others who chooses to use the old gods in their ceremonies like to believe.
The other blot ceremonies of the year.
We start with Goa blót the month of Gói comes after Thorri and starts on the 14th of February. In the Founding of of Norway in Orkneyinga saga its says:
One spring by þorrablót it happened that Gói was lost. They searched for her, but could not find her. When the month had gone, Thorri let the blot continue and now they made blot to find out where she had gone. The called it góiblót. But they still did not get to know where she was.
Snorri says that the disirting in Uppsala was in the month of Gói . This is also told about by Adam of Bremen. But he places the time in or near the spring equinox. There is not really much of a contradiction in this, as the equinox was earlier on the Julian calendar than in the Gregorian calendar we use today. And it can’t be ruled out that the great blót in Uppsala was held at the first full moon in the month of Gói. In a footnote on the Orkneyinga saga it says that Gói was sometimes called the “horning month” as that was when the deer shed their antlers, and it was the time in heathen times of the great blót in Uppsala.
“The traditions that is connected with Thorri and specially Gói is all about fertility, often birth, marriage and growth. The names are ancient, and there is still a rich tradition connected with them in rhymes, verses and weather marks” (Sandal 2006)
In the beginning of winter Sigvat Skald left for Götaland in Sweden according to Heimskringla. The beginning of winter must have been in late october or in November. Perhaps in the beginning of the month of Ylir that starts in mid november. It was a bad time to travel, because in every farm they came to, they where denied shelter for the night.
They traveled trough Götaland, and came in the evening to a farm called Hov. There the door was closed, and they could not get inside. The people in the house said it was a holy place.
I came to Hov as it happened
The door was locked. I asked
from outside, curious stuck my nose in
I got short words back
they called the place holy.
I asked the gygri to take them
heathen folk me chased
Then he came to another farm. There the House Wife stood in the door and said that he must not come inside, she said they held alfablót.
Sigvat was denied shelter at two more farms in the area until i finally came to Ragnvald Jarl. This goes contradictory to all rules of hospitality of the age. After all in
Hávamál it clearly say how to greet, and take care of guests. So the Alfablót must have been a very private affair, kept within the family, as opposed to the great public blótveizla of Vetrnætr, hokunótt and sumarmål.