FC" wrote in message
...
B1 and C1 will alternate ( one of the 2 is empty while the other has a
value)

If that is the case then and the cells are truely empty not just showing an
empty string then:

=A1+B1-C1

will work because the empty cells will be treated as zero values.

--
HTH

Sandy
In Perth, the ancient capital of Scotland
and the crowning place of kings


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"FC" wrote in message
...
I need a double formula if that's possible.
1 Worksheet A,B,C,D from 1 to 100 all columns.
For explanatories purposes I ll use just the first row ( formula will be
copied down to 100)
D1=A1+B1
but if there is not value in B1, then it will be a value in C1 and the
formula instead of adding will sustract. D1=A1-C1
A1 will always has a value
B1 and C1 will alternate ( one of the 2 is empty while the other has a
value)
D1 will be the total, either from adding B1 or sustracting C1( depending
who
has the value) from A1.
Legend : value= number
XL 2003