An online age calculator is a tool or website that allows users to calculate someone's age based on their birth date and the current date. It provides a convenient way to determine a person's age without manually performing the calculations or counting the years, months, and days.

It's important to note that online age calculators rely on accurate input of birth dates and current dates, as well as correct handling of leap years and different calendar systems. The precision of the calculated age may also depend on the specific algorithms and calculations used by the age calculator tool or website.