Day By Day: How Dates Work In Excel


Ah, 1900... a good year.  L. Frank Baum publishes The Wonderful Wizard of Oz, Max Planck discovers quantum physics, and Louis Lassen invents the hamburger.

This also happens to be the year when Excel starts calculating dates!  But Excel doesn't exist yet, so how...?

Microsoft Excel records dates with a serial number.  Each incremental integer represents the number of days since January 0, 1900.

So the number 1 represents January 1, 1900.  The number 7 represents January 7, 1900.  The number 16229 represents D-Day from World Way II, June 6, 1944.  And the number 37145 represents the day the World Trade Center towers fell, September 11, 2001.

There's nothing special you need to do in order to get Microsoft Excel to record dates this way or show serial numbers as dates.  It's just important to know how Excel works behind the scenes because many of the formulas we use on these serial numbers.  We can even "subtract" dates!

So to recap, if you need to record a date in a cell, best to go with the mm/dd/yyyy format.  Excel will display it that way, but behind the scenes it's stored as a counter from good ol' 1900!

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