A küatun (, ) is a unit of time in the Maya calendar equal to 20 tuns or 7200 days, equivalent to 19.713 tropical years. It is the second digit on the normal Maya long count date. For example, in the Maya Long Count date 12.19.13.15.12 (December 5, 2006), the number 19 is the küatun. There are 20 k'atuns in a baktun.
The end of a küatun was marked by numerous ceremonies and, at Tikal, the construction of large twin pyramid complexes to host them. The küatun was also used to reckon the age of rulers. Those who lived to see four (or five) küatuns would take the title 4-(or 5-)küatun ruler. In the Postclassic period when the full Long Count gave way to the Short Count, the Maya continued to keep a reckoning of küatuns, differentiating them by the Calendar Round date on which they began. Each küatun had its own set of prophecies and associations.