A Birthday Calculator is a tool that helps individuals determine their age in years, months, and days based on their birth date. By inputting the date of birth, the calculator can quickly provide the exact age, making it useful for various purposes, such as planning celebrations or understanding age-related milestones. Additionally, some birthday calculators offer features like calculating zodiac signs or determining the day of the week a person was born. These calculators can be found online or as mobile applications, providing a fun and informative way to celebrate one's special day and learn more about personal astrology or numerology.