counting months from dates

PERSON: Dave PRJ A
Col. b Col. c Col M
row18 4/1/2004 5/1/2004 50%
row19 5/1/2004 2/1/2005 10%
row20 2/1/2005 4/1/2005
row21 4/1/2005 9/1/2005 10%

I am trying to calculate the number of months between
4/1/2004 to 9/1/2005 but if there is no value or 0 in
Collumn M then to exclude counting those associated months
e.g. in this case period 2/1/2005 to 4/1/2005.

Thanks in advance!

Hi
try the following (works only for complete months)
=SUMPRODUCT((M1:M100"")*(M1:M1000),(MONTH(C1:C 100)-MONTH(B1:B100)))


--
Regards
Frank Kabel
Frankfurt, Germany

"newbie" schrieb im Newsbeitrag
...
PERSON: Dave PRJ A
Col. b Col. c Col M
row18 4/1/2004 5/1/2004 50%
row19 5/1/2004 2/1/2005 10%
row20 2/1/2005 4/1/2005
row21 4/1/2005 9/1/2005 10%

I am trying to calculate the number of months between
4/1/2004 to 9/1/2005 but if there is no value or 0 in
Collumn M then to exclude counting those associated months
e.g. in this case period 2/1/2005 to 4/1/2005.

Thanks in advance!