Q: Why do I see a 53rd week on my week based reports?
A: The ISO date standards dictate that weeks start on their Mondays and the year that they belong to is given by the year in which their Thursday falls. As a result, there are certain years that have a 53rd week. For example, since 2020 was a leap year and started on a Wednesday, there are 53 weeks in 2020. 2015 was not a leap year, but Jan 1, 2015 fell on a Thursday and therefore has 53 weeks. In general, any regular year that starts on a Thursday, and any leap year that starts on a Wednesday will have 53 weeks. Here are the years between 1970 and 2050 where you will encounter this:
1970 1971 1976 1977 1981 1982 1987 1988 1992 1993 1998 1999 2004 2005 2009 2010 2015 2016 2020 2021 2026 2027 2032 2033 2037 2038 2043 2044 2048 2049