Find 1st blank cell in column & sum to the same row in another col

[Guest]

I am trying to come up with a formula that will accomplish the following.....

I have 2 columns that compare the current year weekly data to prior year's
weekly data. I need a formula that will sum Column D to same week in Column
B. Each week, the next row will be updated in Column B and the cells summed
in Column D need to change to include the next week's data too. So for the
table below, I would come up with the figure of 350 and the next week when B4
has data input, the total for Column D would be 500. I am trying to compare
total inventory each week. The cells in Column B with no data are blank.
Any ideas?
A B C
D
1 week ending 1-6-07 150 wek ending 1-7-06 200
2 week ending 1-13-07 100 week ending 1-14-06 100
3 week ending 1-20-07 75 week ending 1-21-06 50
4 week ending 1-27-07 week ending 1-28-06 150
5 week ending 2-3-07 week ending 2-4-06 225
6

 

[Guest]

Assuming your data starts in row 2, and that the only entries would be the
numbers you want to sum

=sum(offset(d2,0,0,count(b2:b20),1))

Change B2:B20 so that it includes all the rows of possible weekly data. Do
not include the row with the sum formula

 

[T. Valko]

Here's the non-volatile version:

=IF(COUNT(B1:B5),SUM(D1:INDEX(D15,COUNT(B1:B5))),0)

Biff