Not sure what you're looking for but why not just do this:

=STDEV(CO12:CO65536)

Empty cells are ignored but you need at least 2 numbers in the range to
calculate otherwise you get an error.

Or, if you really do want a dynamic range assuming there will be no empty
cells *within* the range and the range contains only numbers:

=STDEV(CO12:INDEX(CO12:CO65536,COUNT(CO12:CO65536) ))


--
Biff
Microsoft Excel MVP


"John" wrote in message
...
Hi everyone, I hope some can help me with this:

I need to run a standard deviation on a range within a column that start
at
CO12 and goes on to dynamically added rows

So far I've tried:

=STDEV(CO12:INDEX(CO:CO,ROW()-1))