Sri Lanka gives a public holiday on every full moon, which is twelve or thirteen days a year decided entirely by the Moon.

Poya days mark the full moon in the Buddhist calendar and each one is a national holiday: shops close, alcohol is not sold, and the date moves with the lunation rather than the calendar. It is the most moon-driven working year of any country — and because a lunar year is about eleven days shorter than a solar one, some Gregorian years get thirteen of them.