How do a add a group of numbers in reverse until a condition is met?

[Water Billing]

I am trying to add a group of numbers together until I reach a 0 in a cell; however, I am starting with the last number in a column and going in reverse.

100

200

300

0

450

200

600

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i.e. I would like to start with the last number (600) and add until I reach a zero (600+200+450). Can someone help me? Thank you.

 

[Marcelo Branco]

Welcome to Mr Excel forum

Try

	A​	B​	C​
1​	Numbers​		Formula​
2​	100​		1250​
3​	200​
4​	300​
5​	0​
6​	450​
7​	200​
8​	600​

Formula in C2
=SUM(INDEX(A2:A8,LOOKUP(2,1/(A2:A8=0),ROW(A2:A8)-ROW(A2)+1)):A8)

Hope this helps

M.