In Excel dates are really just numbers formatted to look like dates.
For example, today is 2/23/2010. If you type that in a cell Excel recognizes
that as a date and automatically applies a date format to the cell. However,
the displayed date is just a format, it's not the true value of the cell. To
see the true value of the cell change the format to either General or
Number. When you do you'll see that the true value of the cell is the number
40232.
That number represents the number of days since a base date. In Excel the
default base date is 1/1/1900. That number value is also known as the date
serial number.
1/1/1900 is date serial number 1
1/2/1900 is date serial number 2
1/3/1900 is date serial number 3
1/4/1900 is date serial number 4
1/5/1900 is date serial number 5
etc
etc
2/23/2010 is date serial number 40232
2/23/2010 is 40,232nd day since the base date of 1/1/1900
So, to count dates you use the COUNT function which counts only numbers.
=COUNT(A1:A10)
