How to calculate age (in years) based on Date of Birth and getDate()

Question

I have a table listing people along with their date of birth (currently a nvarchar(25))

How can I convert that to a date, and then calculate their age in years?

Answer 1

select floor((datediff(day,0,@today) - datediff(day,0,@birthdate)) / 365.2425) as age

There are a lot of 365.25 answers here. Remember how leap years are defined:

• Every four years
  • except every 100 years
    • except every 400 years