Re-tweaked my response involving sumproduct in your earlier posting
(I read liberally between-the-lines in venturing my response)

Try in C1:
=SUMPRODUCT(($A$1:$A$17=A1-$B$1)*($A$1:$A$17<=A1+$B$1))
Copy down

P/s: From your posting profile, you have put in close to 1,100 posts
to-date. That's quite a lot of posts. And you must have received many, many
responses since which helped you resolve your issues and build up your
knowledge along the way. But amazingly, you have yet to help out any other
poster to-date?
--
Max
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xdemechanik
---
"Eric" wrote:
[Re-word my post]
Does anyone have any suggestions on how to determine the frequency?
There is a list of date under column A, and a given number 3 in cell B1
I would like to determine the frequency with +/- 3 days acceptable range

04-Jan-09, 09-Jan-09, 11-Jan-09, 18-Jan-09, 20-Jan-09, 22-Jan-09,
23-Jan-09, 24-Jan-09, 24-Jan-09, 24-Jan-09, 24-Jan-09, 26-Jan-09,
27-Jan-09, 05-Feb-09, 06-Feb-09, 12-Feb-09, 17-Feb-09 ...

On 4-Jan-08, it should return 1 in cell C1 for range between 1-Jan-09 and
7-Jan-09, which include 04-Jan-09 only.

On 09-Jan-08, it should return 2 in cell C3 for range between 5-Jan-09 and
12-Jan-09, which include 09-Jan-09 and 11-Jan-09.

On 11-Jan-08, it should return 2 in cell C3 for range between 8-Jan-09 and
14-Jan-09, which include 09-Jan-09 and 11-Jan-09.

...

On 24-Jan-08, it should return 8 in cell C8 for range between 21-Jan-09 and
27-Jan-09, which include 22-Jan-09, 23-Jan-09, 24-Jan-09, 24-Jan-09,
24-Jan-09, 24-Jan-09, 26-Jan-09, 27-Jan-09