No you can't, and you cannot even use it in SUMPRODUCT because WEEKNUM will
not handle an array of dates. So you have to craft your own

=SUMPRODUCT(--(1+INT(($A$2:$A$20-(DATE(YEAR($A$2:$A$20),1,2)-WEEKDAY(DATE(YEAR($A$2:$A$20),1,1))))/7)=1))

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HTH

Bob


(there's no email, no snail mail, but somewhere should be gmail in my addy)



wrote in message
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I'm trying to use a function (WEEKNUM) as the criteria for a range in
COUNTIF. Is this possible?