The Igbo calendar (Igbo: Ògụ́àfọ̀ Ị̀gbò) is the traditional calendar system of the Igbo people which has 13 months in a year (afo), 7 weeks in a month (onwa), and 4 days in a week (izu) plus an extra day at the end of the year, in the last month. The name of these months was reported by Onwuejeogwu (1981).
Such a calendar was presented by Onasanya (2009) in his The Urgency of Now!: Building a True Nigerian Nation. Many parts of this calendar are named for or dedicated to certain spirits (Igbo: Mmuo) and deities (Igbo: Alusi) in the Igbo mythology. Some of the spirits and deities were believed to have given the Igbo people knowledge of time. The days, also known as market day, also correspond to the four cardinal points, north, south, east, west.
Although worship and spirit honoring was a very big part in the creation and development of the Igbo calendar system, commerce also played a major role in creating the Igbo calendar. This was emphasized in Igbo mythology itself. An example of this is the Igbo market days of which each community has a day assigned to open its markets, this way the Igbo calendar is still in use.
Some Igbo communities have tried to adjust the thirteen month calendar to twelve months, in line with the Gregorian calendar.
The calendar is neither universal nor synchronized, so various groups will be at different stages of the week, or even year. Nonetheless the four-eight day cycle serves to synchronize the inter-village market days, and substantial parts (for example the Nri kingdom) do share the same year-start.
Igbos generally have four market days, namely: eke, orie, afor and nkwo. The market days according to the Igbo calendar follow each other sequentially as shown below:
In various parts of Igboland, each community has a market named after the aforementioned four market days, e.g., Eke market, Afor market.
In the traditional Igbo calendar a week (Igbo: Izu) has 4 days (Igbo: Ubochi) (Eke, Orie, Afọ, Nkwọ), seven weeks make one month (Igbo: Ọnwa), a month has 28 days and there are 13 months a year. In the last month, an extra day is added. The traditional time keepers in Igboland are the priests or Dibia.