Page 279 - Excel 2007 Bible

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Part II
Working with Formulas and Functions
Calculating a person’s age
A person’s age indicates the number of full years that the person has been alive. The formula in the previous
section (for calculating the number of years between two dates) won’t calculate this value correctly. You can
use two other formulas, however, to calculate a person’s age.
The following formula returns the age of the person whose date of birth you enter into cell A1. This formula
uses the YEARFRAC function.
=INT(YEARFRAC(TODAY(),A1,1))
In versions prior to Excel 2007, the YEARFRAC function was available only when the Analysis
NEW FEATURE
NEW FEATURE
ToolPak add-in was installed. The function is now part of Excel 2007.
The following formula uses the DATEDIF function to calculate an age. (See the sidebar, “Where’s the DATE-
DIF Function?”)
=DATEDIF(A1,TODAY(),”Y”)
Where’s the DATEDIF Function?
ne of Excel’s mysteries is the DATEDIF function. You may notice that this function does not appear in the
Odrop-down function list for the Date & Time category, nor does it appear in the Insert Function dialog
box. Therefore, when you use this function, you must always enter it manually.
The DATEDIF function has its origins in Lotus 1-2-3, and apparently Excel provides it for compatibility pur-
poses. For some reason, Microsoft wants to keep this function a secret. The function has been available since
Excel 5, but Excel 2000 is the only version that ever documented it in its Help system.
DATEDIF is a handy function that calculates the number of days, months, or years between two dates. The
function takes three arguments: start_date, end_date, and a code that represents the time unit of interest. The
following table displays valid codes for the third argument. (You must enclose the codes in quotation marks.)
Unit Code Returns
“y” The number of complete years in the period.
“m” The number of complete months in the period.
“d” The number of days in the period.
“md” The difference between the days in start_date and end_date. The months and years
of the dates are ignored.
“ym” The difference between the months in start_date and end_date. The days and years
of the dates are ignored.
“yd” The difference between the days of start_date and end_date. The years of the dates
are ignored.
The start_date argument must be earlier than the end_date argument, or the function returns an error.

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