Is it possible for a cell to have a formula to calculate a default value based on other cells but for a user to be able to change this value WITHOUT losing the cells formula. ?

I think I understand.....

You can't do it directly, however, you can add a "User Input" cell next to the calculating cell...

Then use an IF function to determine whether or not a user has entered any data into the input cell.

You could do it via VBA as well, however I like to stay clear of it whenever possible.

the function would look like this....

A1 is the Calculated Cell
A2 is the user input cell.

A1: IF(A2="",{calculation from other cells},A2)

hmmm good idea - that may help - thanks for that.

No worries ;)