My experience in the US is that week numbering is used principally by finance to keep track of weekly operations, which is usually only payroll. So it makes per

My experience in the US is that week numbering is used principally by finance to keep track of weekly operations, which is usually only payroll. So it makes perfect sense to me that the week containing Jan. 1 should always be week 1 - in fact otherwise is rather unintuitive. This results in some confusion around the new year but this is kind of an intrinsic problem with weekly payroll and is one of the reasons that payroll closing tends to be a specific and somewhat complex process, as the year totals are calculated more or less independently from the pay schedule. Outside of payroll, I have seen very little use of week numbers for any purpose in the US. Far more common to write "the week of Jan. 18" where the date given is typically, but not always, the Sunday or Monday in that week. Week numbers are not displayed on most calendars to most people would be pretty frustrated if you told them a week number.