first day: =IF(ISBLANK(B3),DATEVALUE(MONTH(A3)&"/01/"&YEAR(A3)),"")

last day: =IF(ISBLANK(B3),DATEVALUE(MONTH(A3)+1&"/01/"&YEAR(A3))-1,"")

But it's not clear, when you want first day and when last day!

Regards,
Stefi

€žZbigniew Lewandowski€� ezt Ã*rta:

Hi,

I have sheet:
In A column exist date
In B column exist "x" or null
In C column please bulid formula: first or last day in month only for day if
in column B exist null.

Example:

A B Formula in C kolumn
5/1/05 x
5/2/05 x
5/3/05 first day of month
....
5/28/05 last day of month
5/29/05 x
5/30/05 x
5/31/05 x
6/1/05 first day of month
6/2/05 x
.....
6/29/05 last day of month
6/30/05 x
7/1/05 first day of month

Thanks
Zbych