How many days are in one b'ak'tun of the Maya Long Count?

One b’ak’tun of the Maya Long Count contains 144,000 days. It is a large calendrical unit made up of 20 k’atuns, each containing 7,200 days.

The Long Count uses a modified base-20 system to record elapsed days from a mythical creation date. Its smaller units are the k’in, or day; the winal, of 20 days; the tun, of 360 days; and the k’atun, of 7,200 days. Twenty k’atuns make one b’ak’tun.

The system is not perfectly base 20 because a tun has 18 winals rather than 20. That produces 18 × 20 × 20 × 20 days, or 144,000 days—about 394 solar years. This structure allowed Maya inscriptions to specify dates over periods far longer than the roughly 52-year Calendar Round.

A famous misunderstanding involved December 21, 2012, which marked the completion of the 13th b’ak’tun in one Long Count cycle. It was a calendrical transition, not a prediction of an apocalyptic event. The 360-day tun is therefore not the same as a b’ak’tun.