=SUMPRODUCT(--(C2:C200-A2:A20020))

and

=E1/COUNT(A2:A20)

assuming the first formula is in E1

--
__________________________________
HTH

Bob

"Chas" wrote in message
...
"Issues Log" records date an issue is raised and a target date to complete
action (this being the date raised + 20 days). There is one issue per
row.
I need to count the number of instances where the target date has been
missed, ie where the date completed is more than 20 days after the date
raised. Then I would like to express this as a percentage of the total
issues raised. Can anyone suggest a suitable formula please?

Date Issue Raised Target Date Action Complete
a a+20 a+10
b b+20 b+21
c c+20 c+30

Count if action completed in more than 20 days