db wrote:
In a worksheet with multiple columns of dates, how can I identify any
duplicate dates , if any, among columns. many thanks


One way would be with conditional formatting. Assuming your data is in A1:C100,
select that range, starting with A1, and put the following in the conditional
formatting "Formula is":

=COUNTIF($A$1:$C$100,A1)1

Then select the format you want to use to identify duplicates.