The Maya had a very sophisticated calendar system. It consisted of an almanac which was 260 days, and a 365 day year like ours. In the almanac, also called a tzolkin or count of days, each day had a number from 1 - 13 and one of 20 day names. These were names of gods (see Religion). This was the sacred year. Which ever god was the day name of your birthday, would be your patron deity.
The 365 day year had 18 months of 20 days, and one month of 5 days which were unlucky. On these days they fasted and made sacrifices and didn't do any work they didn't need to do.
What Mayans called days were Kins. After 20 days 1 uinal passed. After 18 uinals, 1 tun passed. 20 tuns is 1 katun.
1 day = 1 Kin
20 Kin = 1 Uinal (20 Days)
18 Uinals = 1 Tun (360 Days)
20 Tuns = 1 Katun (7,200 Days)
20 Katuns =1 Baktun (144,000 Days)
20 Baktuns = 1 Pictun (2,880,000 Days)
This system, called the long count, allowed them to keep an accurate
record of time for thousands of years.
Only priests could truly know which day it was and when things like holidays would happen.