What is the formula for age in Excel?

Put the date of birth into a cell., say cell B2 Then put the following formula into another cell.

=INT((TODAY()-B2)/365.25)

First it takes the date of birth from today's date. That gives a number of days. To take account of leap years, that total is then divided by 365.25 to convert it into years. As we generally think of your age as being what you were at your last birthday, we use the INT function to get the whole number part of your age.