How can I count the number of months it takes to reach a total of 100,000.
This would in a row count fashion from left to right.

Eg.
Cells A1:A7 contain sales by month.
Cell A8 has a count of the number of months where the cumulative sum is
equal to or greater than 100,000. So;

10000, 10000, 40000, 35000, 10000, 10000, 10000

The count would be 5

Also if

0, 0, 0, 50000, 50000, 40000,40000, 40000

The count would be 2 as it ignore 0's to the left of the first value.

Bruce