Enter a date of birth, and optionally a date to measure to, for an exact age in years, months and days. You also get the total in weeks, days and hours, the day of the week you were born, and how long until the next birthday.
Whole years are counted first, then whole months, then the remaining days. This matches how people describe age in conversation and handles month lengths and leap years correctly.
In non-leap years the anniversary is treated as 1 March, which is the most common legal convention. The calculator counts the completed year either way.