A perpetual calendar is a highly sophisticated complication in watchmaking that automatically adjusts for the varying lengths of months and leap years, ensuring the accurate display of the date without manual correction. This intricate mechanism is designed to account for the 30- and 31-day months, as well as the 28-day month of February and the additional day in leap years, following the Gregorian calendar. Typically, a perpetual calendar watch will not require any adjustment until the year 2100, which is a leap year exception in the Gregorian calendar.

The complexity of a perpetual calendar lies in its intricate gear train and cam system, which work in harmony to track the passage of time accurately. This complication is often found in high-end luxury watches and is a testament to the watchmaker's skill and precision. It is considered one of the most prestigious and challenging complications to design and manufacture, often paired with other complications such as moon phases or chronographs.

Perpetual calendar watches are prized for their technical mastery and elegance, offering both functionality and a demonstration of horological expertise. Collectors and enthusiasts value these timepieces for their ability to maintain precise timekeeping over decades, reflecting the pinnacle of watchmaking craftsmanship.