Determine percentage of target based on two dates

I'm really interested in the accuracy for delivering on time, thus my focus has been on the target date (when I said I would deliver) vs. the complete date (the date I did deliver). Here is more detail:

For example, if the Target column date was 03/31/11 and the Complete
column date 03/31/11, then the Metric column would read as "1.00". If
the Complete column was any date sooner than the Target date, the
Metric would be higher than "1.00"; for a Complete date later than the
Target date, such as 04/06/2011, then the Metric would be under than
"1.00"


Target = K4 (mm/dd/yy)
Complete = L4 (mm/dd/yy)
Metric = M4 (0.00%)


NOTE: My metrics have been provided to me, now I'm trying to determine how to capture that information. Perhaps I need to adjust my approach. I've attached a partial screenshot of my spreadsheet.

To calculate your metric we will use

(Target Duration-Actual Duration)/Target Duration

or

=((K4-J4)-(L4-J4))/(K4-J4)

This looks like a job-type of thing, so I'm going to suggest you count only working days for durations.

=(NETWORKDAYS(J4,K4)-NETWORKDAYS(J4,L4))/NETWORKDAYS(J4,K4)

1.0 means you are exactly on target; lower means worse, higher means better. (This is analogous to the Schedule Performance Index used in Earned Value Measurement System.)

Is that what you want to show up in your Metric column? Or do you want the word that indicates the range that this number falls into? The problem with "Outstanding" is that it aggregates multiple items, and I don't know what you want to aggregate. (The others are meaningful just for a single item.)

As NBVC noted it would help if you could show what results you are looking for.