I need to make a sheet, For particular column if i add date  17/11/2016 and other column add formula like D6+30

So the result should be 17/12/2016 => current date plus 30 days addition.

what should i do whenever i add formula the result is cames  #VALUE

17/10/201     =D6+30(Enter) 

Need result 16/11/2016