Every four years, February gains an extra day to keep our calendar in sync with Earth's orbit around the sun. While this keeps the seasons aligned, it introduces a subtle complication when calculating someone's exact age.
If you were born on February 29th, your actual birthday only occurs once every four years. Most systems handle this by treating March 1st as your birthday in non-leap years, but this convention isn't universal.
AgeCalc Pro accounts for leap years automatically, so your age is always calculated precisely down to the day, regardless of when you were born.