What was the name of the Aztec solar calendar of 365 days?

The Aztec solar calendar of 365 days was called the xiuhpōhualli, commonly written Xiuhpohualli.

The name comes from Nahuatl words meaning “year count.” This agricultural calendar contained 18 periods of 20 named days, followed by five additional days called nēmontēmi. The five-day ending was regarded as inauspicious, so the calendar had 365 days but no leap-day system comparable to the modern Gregorian calendar.

The xiuhpōhualli worked alongside the 260-day tōnalpōhualli, or ritual day count. When the two cycles were combined, their pattern repeated every 52 years in a period often called the calendar round. This cycle shaped religious observances, agricultural timing, and the naming of years.

A common mistake is to call the famous Aztec Sun Stone itself the calendar. The stone is a monumental sculpture containing calendrical and cosmological imagery, but the actual 365-day system was the xiuhpōhualli. The 260-day tōnalpōhualli was a separate calendar, not another name for the solar year.