Excel has two date systems, with either a 1900 or 1904 start date: https://support.microsoft.com/en-us/office/date-systems-in-excel-e7fe7167-48a9-4b96-bb53-561

Excel has two date systems, with either a 1900 or 1904 start date: https://support.microsoft.com/en-us/office/date-systems-in-excel-e7fe7167-48a9-4b96-bb53-5612a800b487 https://support.microsoft.com/en-us/office/date-systems-in-e... The original Excel was for the Macintosh and had the 1904 date system, and was later brought to Windows where the 1900 date system was used.