It’s easy to calculate someone’s age from their date of birth if you know about Excel’s DATEDIF function, unfortunately it’s easy to miss this function as it is not documented. I am baffled why it is never included in the list of Excel functions.
To have a formula that updates itself as time goes on you need to get the current date into your formula and you can do this using either the NOW or TODAY functions. There’s no substantial difference between the two functions for this calculation; NOW gives you the current date and time, whereas TODAY just gives the current date. When you enter the function into your formula remember to include the brackets like this, NOW() or TODAY().
So, to calculate someone’s age in years make sure that you have entered their date of birth correctly as a proper Excel date (using slashes or dashes) and then enter the formula:
Where C3 is the cell containing the date of birth. The interval value “y” must be entered in double quotation marks. The age is calculated in whole calendar years and will update on the subject’s birthday. If you want to calculate the exact age and include the months or even the days then you have to change the interval value.