Aztec Calendar Our Calendar We have 365 days in our calendar. One year is 365 days. Unless it is a leap year, like 2020, then it has 366 days. We have 12 months in one year. We have 52 weeks in one year. We have 7 days in one week. The Aztec calendar has 365 days in one year. The Aztecs had 18 months in each year. The Aztecs had 13 days in one week.