How can I convert a date into a Value or Number in excel.?

The formula below returns the of day-of-year (number) for a date in cell A1:

=A1-DATE(YEAR(A1),1,0)

Note: Excel automatically formats the cell with this formula as a date, so change the cell's format to another option (like General).

Excel contains a number of built-in date and time functions. When you want to use one in a cell, simply click the "fx" button to the left of the data entry field and a selection box will pop up. Use the drop-down menu and choose the Date and Time functions and select the one you want from the resulting list. Excel will guide you through the application of the function. When you are done, simply click the check mark.

if you want

1/1/2009 = 1

1/2/2009 = 2

1/1/2010 = 366

1/2/2010 = 367

the formula is

=A1-DATE(2008,12,31)