Maintaining a value unless replacement available

[RyanHarrison]

I can't figure out how to do this (hopefully I explain it correctly):

I've got 2 cells, we'll call them cell A and cell B. I want to be able to put a number into cell A and have it stay there as long as cell B is blank. Once a number is placed into cell B, however, I want that number to override what has been placed in cell A.

I've been trying to use IF statements that basically say (loosely): "IF cell B is blank, then leave cell A as is, otherwise use what's in cell B (i.e. once I actually put a number in cell B, it should overwrite what's in cell A)," but I dont know how to write this or if it's possible.

[shg]

Welcome to the forum.

=If(B="", some expression using A, some expression using B)

Please read the Forum Rules about thread titles before starting your next thread.

[RyanHarrison]

My problem is that I dont know what the "expression using A" or "expression using B" would actually be.

Cell A is an estimated rate of return and Cell B is an ending balance. I want to run calculations off of the estimated rate of return that I put in Cell A as long as Cell B is empty. Once I put in a final ending balance for Cell B, I want to compute a final rate of return and have that replace the estimate that is in Cell A.

[shg]

Call cell A "estimated" and cell C (wherever the formula appears) "final".

You can't enter a value in cell A and then have a formula that changes its value (at least not without a circular reference and interation).