A date complication shows the date (day of month). It can also be part of a comprehensive calendar complication.
A simple date display is extremely simple, advancing a disc or hand once every two revolutions of the hour hand. Many watches feature both day and date, and some have more complicated calendar functions, including month and even year.
The date display typically uses a simple wheel mechanism with each date from 1 to 31 written on a disc and viewed through an aperture in the dial. In a simple date mechanism, the wearer must manually advance the date on months with 28, 29, or 30 days. A mechanism that can keep track of these monthly differences is called an annual calendar or perpetual calendar.
The date can also be displayed by pointer, with a hand indicating the current date using printing on the dial. Date by pointer is often central to the dial using a decorative hand, often with a sun or moon at the tip.