=AVERAGE(A2:A200-A1:A199)

Commit with Shift+Ctrl+Enter (array formula)

HTH
Kostis Vezerides

On Apr 4, 6:41 pm, Jman wrote:
A1:A200
01/07/08
07/07/07
04/23/07
11/30/06

C1: I need average days between dates, considering leap years.

And is it possible to format C1 to equal.."2 month 3 days"
Thanks.