The Maya had a vigesimal (base-20) system and so often years in multiples of 20 were celebrated. A 20-year period is called a K'atun in classic Mayan. Maya kings would often erect a stelae (a carved, free-standing stone) in commemoration for each k'atun they had been king. For instance, one of the kings of the Maya city of Palenque, Pakal, lived past 80 and so erected three stelae during his rule to commemorate each k'atun. Pakal also adopted the title of "3-k'atun lord" after his third k'atun as king.

As for important dates, the long-count cycle used to record most dates on Maya monuments began on the day August 11, 3114 BCE. In the Maya calendar, this would be rendered as 13.0.0.0.0 and the next day rendered as 0.0.0.0.1 (i.e. one day past the start date). This combination of base 20 (a 400 year period called a bak'tun) with the number 13 (so 13 bak'tuns) seems to be significant. 13 is a number that crops in Mayan religious texts fairly often, usually associated with the 13 layers of the upper world. Normally, you would count to 20 sets of bak'tun (so 20x400 years), but in the case of the starting date there are only 13 bak'tun instead of the 20 you would expect from a vigesimal system.

In addition to the base 20 long-count calendar used by the Maya to records years, a repeating 260-day ritual calendar was used called the tzolk'in or "count of days". The tzolk'in consisted of 20 named days that were numbered 1-13 sequentially (so the day 1 Imix is followed by 2 Ik followed by 3 Akbal, etc...). This means that if you start on 1 Imix, no day and number combination repeat until 260 days later. People were often named after the day they were born on. Additionally, the 260 day period had some significance since it is roughly the duration of human gestation and has some relation to the agricultural cycle.