Nemontemi

In the Aztec culture, the Nahuatl word nemontemi refers to a period of five intercalary days inserted between years of the Aztec calendar. Each of the 18 Aztec "months" had 20 days, for a total of 360 days. The nemontemi accounted for the remaining 5 days of the approximate tropical year. According to the research by R. C. Tunnicliffe, the Aztecs dealt with the remaining fractional-day discrepancy with the true tropical year length by adding a "trecena" (13 days) after each bundle of 52 years; these 13 days were not considered unlucky, but they were not characterized by the features (numbers and symbols) of the Aztec calendar.

The word nemontemi means "useless days" or "unlucky days"; Spanish lexicographers glossed it as "dias baldios", "wasted days". They were considered to bring ill fortune, and most activities (including even cooking) were avoided if possible during the nemontemi.

R. C. Tunnicliffe, Aztec Astrology. This work shows how the Nemontemi days are calculated for each current year (around 5 to 10 of April every year).

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