Why are Excel weekdays wrong for 1900?
- by Jeroen Wiert Pluimers
This question is based on the observations of AdamV in his answer on How do I get the day name into a cell in Excel?
When A1 has the value 2009-08-01, then:
=WEEKDAY(A1) will obtain 7
=TEXT(7, "dddd") will obtain Saturday
=TEXT(7,"dddd, yyyy-mm-dd") will obtain Saturday, 1900-01-07
=TEXT(1,"dddd, yyyy-mm-dd") will obtain Sunday, 1900-01-01
=TEXT("1900-01-01","dddd, yyyy-mm-dd") will also obtain Sunday, 1900-01-01
The last two are wrong: the 1st of January 1900 is actually a Monday.
Various sources seem to confirm that:
January 1900 - Wikipedia, the free encyclopedia.
Year 1900 Calendar – The Netherlands.
Year 1900 Calendar – United States.
What am I missing? Why is Excel doing this wrong?