Forum Discussion
Date Format in Excel
totzelberger Search on-line for "dates before 1900 Excel" and you will understand that working with pre-1900 dates in Excel isn't very straight-forward. I haven't come across a method yet that allows you to enter numbers like yours and automatically transform them to real dates. With text functions like LEFT, MID, RIGHT, CONCAT (or TEXTJOIN if your Excel version supports it), you can fairly easily create text strings that look like dates in the mm/dd/yyyy format, but they will never be seen as real dates in Excel.
=TEXTJOIN("/",,TEXT(LEFT(C2,LEN(C2)-6),"00"),MID(C2,LEN(C2)-5,2),RIGHT(C2,4))or
=CONCAT(TEXT(LEFT(C2,LEN(C2)-6),"00"),"/",MID(C2,LEN(C2)-5,2),"/",RIGHT(C2,4))
Enter one of these in e.g. H2 and copy down. This will turn 6091854 into 06/09/1854
And if you want to perform calculations based on the dates, you'll need some more tricks as shown in the attached link.
https://www.mrexcel.com/excel-tips/deal-with-dates-before-1900/