What’s the Excel 1900 or 1904 Date System?

An interesting question came into us the other following a course. It was regarding Excel and the 1904 Date System.

One of the subjects we cover on our courses is the importance of entering dates in an acceptable form when adding them into a cell. Otherwise you will be unable to use them in a calculation or sort.

All dates should be equivalent to a serial number.

If you work on a PC and windows the default numbering system starts on 1st January 1900 – that is day 1 and so forth.

On a Macintosh computer it all starts 2nd Jan 1904. This is the default system. It seems Macintosh decided this was a better system. This design was intended to prevent problems related to the fact that 1900 was not a leap year.

Of course they can be changed. The Excel options will allow us to change to the 1904 system on a PC if that is required.

What to remember.

  • If you have entered dates into a workbook using the 1900 date system and then you switch to the 1904 date system, then all your dates will be out by 4 years.
  • You should be very careful if you are using different date systems in two linked workbooks as the same serial numbers will be interpreted as different dates.

I have a feeling this could make a good pub quiz question as not many people will know about this.

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