Methodology
The calculator compares the calendar components of the birth date and target date to return completed years, months and days. This avoids assuming that every year has 365 days or every month has the same length.
Example
Example: a person born January 15, 2000 has an exact calendar age of 26 years, 7 months and 24 days on September 8, 2026.
The calculator follows the standard Gregorian calendar leap year rule: a year is a leap year if it's divisible by 4, except century years, which must be divisible by 400. That's why 2000 was a leap year but 1900 was not, and it's why a simple "365.25 days per year" shortcut can drift slightly off from someone's real calendar age over time.
Edge case example
Someone born on January 31 still gets a birthday every month-end in months without a 31st — the calculator resolves this by counting to the last valid day of that month rather than skipping over it.