Watches with a moon phase display can show phases, such as new moon or full moon, on the display. This requires only the input of the local time and a so-called tidal interval, and the phases can be displayed for any date, even in the future. In addition to the moon phase, the moon age is also displayed. 

Anglers use this function, for example, to identify tendencies for the biting behaviour of certain fish. In addition, moon phases have an influence on the development of high and low tides.