I live in Europe. Week starts on Monday and ends on Sunday. Today is Friday, the 5th day of the week.

CodePudding user response：

WEEKDAY is returning the correct result in that cell - i.e. 5.

If you format 5 as ddd, you are actually formatting the date 5 days after 31.12.1899 which is the 5th Jan 1900, which was a Thursday.