As Peo pointed out in another post:-

For January you need to add another condition

=SUMPRODUCT(--(MONTH(A1:A100)=1),--(ISNUMBER(A1:A100)))

it's because that excel sees blank cells as zero and excel dates dtart with
January zero 1900 the unary minuses will convert boolean values of true and
false to 1 and 0

http://www.mcgimpsey.com/excel/formulae/doubleneg.html

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Regards
Ken....................... Microsoft MVP - Excel
Sys Spec - Win XP Pro / XL 97/00/02/03

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It's easier to beg forgiveness than ask permission :-)
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"Ron" wrote in message
...
I have been seeing "--" in formulae but cannot find an explanation of what
it is or does.

Example: =SUMPRODUCT(--(MONTH(B2:B13)=1), C2:C13)


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Ron P

Sometimes you're the windshield:)
Sometimes you're the bug:(