Date fill in Excel

I have problem with excel , that is , I want to enter a date in cell like monday,February 19,2007…. Then I want to change this date like
tuesday, February 20,2007
wednesday, February 21,2007
.
.
.

but while dragging it is changed as
monday,February 19,2008
monday,February 19,2009
monday,February 19,2010…

If anyone know about this please help me…
my email id is aprafeeq@gmail.com