A k'atun or k'atun-cycle is a unit of time in the Maya calendar equal to 20 tuns or 7,200 days, equivalent to 19.713 tropical years. It is the 2nd digit on the normal Maya long count date. For example, in the Maya Long Count date 184.108.40.206.12 (December 5, 2006), the number 19 is the k'atun.
The end of the k'atun was marked by numerous ceremonies and at Tikal the construction of large twin pyramid complexes to host them. The k'atun was also used to reckon the age of rulers. Those who lived to see four (or five) k'atuns would take the title 4-(or 5-)k'atun lord. In the Postclassic period when the full Long Count gave way to the Short Count, the Maya continued to keep a reckoning of k'atuns, differentiating them by the Calendar Round date on which they began. Each k'atun had its own set of prophecies and associations.