OK, here's a little further info and a (hopefully) more simplified explanation of what I'm stuck on. I really hope someone can help, I know I'm close but I'm just not quite there yet.

I need to calculate an end result, that is based on a gradually increasing set of numbers, depending on the numbers of times (days) I choose to run the claculation for.

Example:

On day 1, X=A+B

On Day 2, B=B+C and so now X=X (previously defined as A+B)+B

On Day 3, B (previously defined as B+C) now = (B+C)+C and so, X=X+B

and so forth... each time, the updated X value needs to have the previously updated B value added to itself, yielding an ever increasing series of numbers. One more example using actual numbers:

A=1.00

B=.50

C=.02

When T (my time variable) = 0,

X=1.00

T=1

X=1.50 (A+B)

B=.52 (B+C)

T=2

X=2.02 (X+B)

B=.54 (B+C)

And so forth...

How on earth can I calculate this in a single formula? I can do it already with a zillion different cels, one for each possible time increment, and it works fine. But this would ultimately leave me with THOUSANDS of individual cels being used and I want to avoid that.

I've played with arrays but haven't been able to get them to work. Also noticed that Excel doesn't allow much in the way of looping outside of if/then logic, unless you delve into VB which I am totally unfamiliar with.

Thanks in advance for any help... this has been a thorn in my side for several days now.

Jonathan

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