The idea of a 13th month is both fascinating and perplexing. In most of the world, the calendar system is based on the familiar twelve-month Gregorian calendar.
However, throughout history and across different cultures, alternative calendars have been developed—some of which include a thirteenth month. Understanding what the 13th month is called, where it is used, and why it exists requires a look at various calendar systems and traditions.
The Gregorian Calendar: Why Only 12 Months?
The Gregorian calendar, introduced by Pope Gregory XIII in 1582, is the internationally accepted civil calendar. It consists of twelve months, each with a set number of days, totaling 365 or 366 days in a leap year.
The months are named January, February, March, April, May, June, July, August, September, October, November, and December.
Most people are familiar only with these twelve months, but this system is not universal. The Gregorian calendar was designed to approximate the solar year, aligning with Earth’s orbit around the sun.
However, not every culture has followed this system throughout history.
Calendars with 13 Months: An Overview
While the twelve-month calendar is dominant, a number of societies have used or continue to use calendars featuring a 13th month. These calendars often arose from different religious, agricultural, or astronomical needs.
Some of the most prominent examples come from Ethiopia, ancient Egypt, and proposed reform calendars like the International Fixed Calendar.
The reasons for adding a 13th month vary. Some calendars are lunar or lunisolar, trying to align months with moon cycles, which result in a year longer than 12 lunar months but shorter than 13 solar months.
Others seek to correct imbalances or improve consistency.
The Ethiopian Calendar: Pagumē, the 13th Month
In Ethiopia, the official calendar is not the Gregorian calendar but the Ethiopian calendar, which is closely related to the ancient Coptic calendar. This calendar is unique in having thirteen months in each year.
The name of the 13th month in Ethiopia is “Pagumē” (sometimes spelled Pagume or Pagumen). Pagumē is a very short month compared to the others.
It usually has five days but has six days in leap years.
“Pagumē is a time of spiritual reflection and is considered by many Ethiopians to be a period of renewal and transition.”
— Ethiopian Calendar Scholar
| Month Number | Month Name | Days |
|---|---|---|
| 1 | Mäggabit | 30 |
| 2 | Miyazya | 30 |
| 3 | Genbot | 30 |
| 4 | Säne | 30 |
| 5 | Hamle | 30 |
| 6 | Nehasse | 30 |
| 7 | Meskerem | 30 |
| 8 | Tekemt | 30 |
| 9 | Hedar | 30 |
| 10 | Tahsas | 30 |
| 11 | Tir | 30 |
| 12 | Yekatit | 30 |
| 13 | Pagumē | 5 or 6 |
Pagumē is unique in that it serves as a way to synchronize the calendar with the solar year. The other twelve months each have 30 days, totaling 360 days.
Pagumē’s 5 or 6 days compensate for the difference between that total and the actual length of the year.
The Coptic Calendar: Nasi, the 13th Month
The Coptic calendar, also known as the Alexandrian calendar, is used by the Coptic Orthodox Church and is similar to the Ethiopian calendar. In this system, the 13th month is called Nasi (or “Nasie”).
Like Pagumē, Nasi is a short month, usually consisting of five days, or six in leap years. The Coptic calendar divides the year into twelve months of 30 days, with Nasi making up the remainder.
| Month Name | Number of Days |
|---|---|
| Thout | 30 |
| Paopi | 30 |
| Hathor | 30 |
| Koiak | 30 |
| Tobi | 30 |
| Meshir | 30 |
| Paremhat | 30 |
| Paremoude | 30 |
| Pashons | 30 |
| Paoni | 30 |
| Epip | 30 |
| Mesori | 30 |
| Nasi | 5 or 6 |
The existence of Nasi allows the Coptic calendar to remain aligned with the solar year. Both the Ethiopian and Coptic systems demonstrate the practical use of a 13th month in calendar design.
The French Revolutionary Calendar: Sansculottides
During the French Revolution, a radical new calendar was introduced: the French Republican (or Revolutionary) Calendar. This system sought to de-Christianize timekeeping and create a more rational structure.
The calendar consisted of twelve months of 30 days each, followed by a short period of 5 or 6 days known as the Sansculottides. Although not officially considered a 13th “month,” the Sansculottides served a similar purpose, bridging the gap between the 360-day months and the actual solar year.
“The Sansculottides were days of celebration, reflecting the values of liberty, equality, and fraternity.”
— Historian of the French Revolution
Each Sansculottides day had a distinct name and was dedicated to virtues like reward, labor, and opinion. In leap years, a special day called the “Day of the Revolution” was added.
The International Fixed Calendar: Sol, the Proposed 13th Month
In the 20th century, some reformers proposed alternative calendars to simplify date-keeping. One of the best-known is the International Fixed Calendar, designed by Moses B.
Cotsworth in 1902.
This calendar divides the year into thirteen months of exactly 28 days each. The name of the 13th month in this system is Sol.
| Month Number | Month Name |
|---|---|
| 1 | January |
| 2 | February |
| 3 | March |
| 4 | April |
| 5 | May |
| 6 | June |
| 7 | Sol |
| 8 | July |
| 9 | August |
| 10 | September |
| 11 | October |
| 12 | November |
| 13 | December |
In this arrangement, every month has exactly four weeks, making the calendar regular and predictable. An extra day, called “Year Day,” is added outside the week structure to keep the calendar aligned with the solar year.
The International Fixed Calendar was used by some organizations, including Eastman Kodak Company, for business purposes in the 20th century. However, it never gained widespread acceptance.
Other Calendars and Concepts of a 13th Month
Besides the major examples above, other cultures and proposals have incorporated a 13th month in various ways. Lunar calendars, for instance, occasionally introduce an extra month to correct discrepancies between lunar cycles and the solar year.
In the Hebrew calendar, a lunisolar system used for Jewish religious purposes, a 13th month called Adar II (Adar Sheni) is inserted seven times every 19 years. This process is known as “intercalation” and ensures that festivals remain in their appropriate seasons.
| Month Number | Month Name |
|---|---|
| 12 | Adar |
| 13 | Adar II (Adar Sheni) |
The addition of Adar II keeps the calendar in sync with the solar year, preventing holidays like Passover from drifting into the wrong season.
Similarly, in ancient Babylonian and other Mesopotamian calendars, an extra month was sometimes added by royal decree to ensure agricultural and religious events aligned properly.
Why Do Calendars Add a 13th Month?
The primary reason for the existence of a 13th month in various calendars is the difference between the lunar and solar cycles. A lunar month (the time between new moons) is about 29.5 days, so twelve lunar months add up to only about 354 days—some 11 days short of a solar year.
To keep lunar-based calendars in harmony with the solar year and the seasons, an extra month must occasionally be added. This process is called intercalation.
It prevents holidays and important events from gradually shifting through the seasons.
“Intercalation is a vital tool for maintaining the accuracy and relevance of lunar and lunisolar calendars.”
— Calendar Systems Expert
Some calendars, like the Ethiopian and Coptic, formalize this process by always including a short 13th month. Others, like the Hebrew calendar, add the 13th month only in certain years.
How the 13th Month is Celebrated or Used
In systems where the 13th month is always present, such as the Ethiopian calendar, it often takes on special significance. Pagumē, for example, is considered a time of transition, reflection, and sometimes celebration.
In calendars where the 13th month is added only occasionally, it is generally treated as a regular month, although its presence ensures that religious and cultural observances occur at the correct times.
The French Sansculottides were a time of civic festivals, while the International Fixed Calendar’s Sol would have functioned as a regular month, had the calendar been adopted.
Modern-Day Relevance and Curiosities
The concept of a 13th month is intriguing in a world where timekeeping is largely standardized. While most countries and organizations adhere to the Gregorian calendar, the persistence of systems with 13 months demonstrates the diversity of human approaches to organizing time.
For example, Ethiopia celebrates its New Year in September, and the country’s calendar is about seven to eight years behind the Gregorian count. Tourists and business travelers often find this offset—and the existence of Pagumē—fascinating.
In Israel and among Jewish communities worldwide, the appearance of Adar II in “leap years” can affect the timing of major holidays and rituals.
These examples remind us that our system of measuring time is not as universal as it might seem. Different cultures have found creative ways to address the natural irregularities of the lunar and solar cycles.
Summary Table: 13th Month Names in Different Calendars
| Calendar | 13th Month Name | When Used |
|---|---|---|
| Ethiopian | Pagumē | Every year (5 or 6 days) |
| Coptic | Nasi | Every year (5 or 6 days) |
| French Revolutionary | Sansculottides | Every year (5 or 6 days, not a true month) |
| International Fixed Calendar | Sol | Proposed, never widely adopted |
| Hebrew | Adar II | 7 times in every 19 years |
| Ancient Babylonian | Varies | Occasionally by decree |
Frequently Asked Questions
| Question | Answer |
|---|---|
| Is there a 13th month in the Gregorian calendar? | No, the Gregorian calendar only has 12 months. |
| What is the most famous 13th month? | Pagumē in the Ethiopian calendar is arguably the most well-known. |
| Why do some calendars include a 13th month? | To align lunar or lunar-solar cycles with the solar year. |
| Does any country currently use a 13-month calendar? | Yes, Ethiopia officially uses a 13-month calendar. |
| What is the name of the 13th month in the Coptic calendar? | Nasi (or Nasie). |
| Are there proposals to add a 13th month to the modern calendar? | Yes, the International Fixed Calendar proposed adding “Sol” as the 13th month, but it was never widely adopted. |
Conclusion: The Name and Significance of the 13th Month
The 13th month is more than just a curiosity or a quirk of history. In systems like the Ethiopian and Coptic calendars, it is a practical solution to the mismatch between lunar and solar cycles.
The most well-known 13th month names include Pagumē (Ethiopian), Nasi (Coptic), Sol (International Fixed Calendar), and Adar II (Hebrew).
These alternative calendars highlight the ingenuity of human societies in adapting to the rhythms of nature. Whether through regular use, as in Ethiopia, or occasional adjustment, as in the Hebrew calendar, the 13th month serves a vital function in ensuring that human traditions, agriculture, and religious observances remain in harmony with the cosmos.
Next time you ponder the passage of time or glance at your calendar, remember that there are many ways to measure a year—and for millions of people, the 13th month is an essential part of life.
