I am using the function apply.weekly() from the xts package and I realized that for the program the week starts Tuesday. So for instance, with a series like this: Close 2006-07-03 36666.00 2006-07-04 36738.00 2006-07-05 36207.00 2006-07-06 36534.00 2006-07-07 36434.00 2006-07-10 36588.00 2006-07-11 36210.00 2006-07-12 36298.00 2006-07-13 35774.00 2006-07-14 35445.00 2006-07-17 35286.00 2006-07-18 35183.00 ... Where 2006-07-03 was Monday. With this command: p <- apply.weekly(Close,first) Here is the series computed: [,1] 2006-07-03 36666.00 2006-07-10 36738.00 2006-07-17 36210.00 ... p <- apply.weekly(Close,mean) [,1] 2006-07-03 36666.00 2006-07-10 36500.20 2006-07-17 35802.60 ... Is there any command to set the week starting from Monday? Thanks Giuseppe