SELECT DATEDIFF(dd,'2014-03-14', '2014-04-06') AS CountOfDaysBetweenDates
More:
DATEDIFF[
^]
[EDIT]
SELECT CONVERT(VARCHAR(7),entry_date,121) AS PeriodOfTime, COUNT(*) as footfall, sum(amount)/(SELECT DATEPART(dd, DATEADD(dd, DATEPART(dd, DATEADD(mm, 1, max(GE.Active_Date))) * -1, DATEADD(mm, 1,max(GE.Active_Date))))) Avgamount
FROM guest_tbl
WHERE entry_date between '2014-03-14' AND '2014-04-06'
GROUP BY CONVERT(VARCHAR(7),entry_date,121)
[/EDIT]