The Flaw with Division Math
A frequent mistake is taking total elapsed days and dividing by 365.25. Because calendar months vary between 28 and 31 days, and leap years occur at distinct intervals, this simple division produces inaccurate fractional ages.
Component-Based Age Calculation
Correct chronological age compares target year, month, and day against birth date parts. When target day is smaller than birth day, days are borrowed from the immediately preceding calendar month.
Legal Age Milestones
In common law jurisdictions, a person reaches an age milestone on the day preceding their birthday or on the stroke of midnight of their birthday date.