"JBrewster" <jTAKEOUTbrewster wrote:
In Column 1 I have 5/1/2013 for about 31 rows,
and in Column 2 have dates beginning with 6/1/2010 (B2)
and moving down about a month at a time so the last row
is B31, with 7/12/2012. Column 3 rows use the formula
=(A1-B1), changing the row listed in the formula for each
row down.
[....]
A31 reads 5/1/2013, B31 reads 7/12/2012, but C31 gives
10/19/1900, not 284 as it should.

Just change the format to General or Number.

First, 7/12/2012 minus 5/1/2013 is 293, not 284. And 10/19/1900 does indeed
correspond to the date serial number 293 (i.e. 293 days after 12/31/1899, as
Excel counts it; Excel thinks 1900 is a leap year).

As to why Excel displayed the result as Date instead of General or Number
only in C31, who knows?

It did not happen in my test. So I suspect the cell had been formatted as
Date before you entered the formula. Anyway, these things happen all the
time: Excel tries to be helpful and intuits what format to use; but
sometimes it is wrong. We just have to make adjustment sometimes.