How many days per month does the Aztec calendar have?

The Aztec calendar consists of two main cycles: the Tonalpohualli, which is a 260-day ritual calendar divided into 20 periods of 13 days, and the Xiuhpohualli, a 365-day solar calendar. The solar calendar is divided into 18 months of 20 days each, plus an additional short month of 5 days, known as "Nemontemi." Therefore, the Aztec calendar has varying numbers of days per month, with most months having 20 days.