The Excel function: DATEVALUE
The DATEVALUE function converts a date that is stored as text to a serial number that Excel recognizes as a date. For example, the formula =DATEVALUE("1/1/2008") returns 39448, the serial number of the date 1/1/2008.
Note The serial number returned by the DATEVALUE function can vary from the preceding example, depending on your computer's system date settings.
The DATEVALUE function is helpful in cases where a worksheet contains dates in a text format that you want to filter, sort, or format as dates, or use in date calculations.
To view a date serial number as a date, you must apply a date format to the cell. Find links to more information about displaying numbers as dates in the See Also section.