It looks nice, although I wonder why you'd treat each line as an independant calculation?

Generally I'd enter an expression, look at the result, then stop. If I wanted to run multiple things I'd use a repl, which would let me copy/paste.

That said it might be useful if you allowed variables to be defined, I updated my own little repl/calculator to allow that recently and found it very useful:

      calc> rent = 700.00
      700
      calc> fee = 92.00
      92
      calc> ( rent - fee ) * 12 
      7296

Allowing that makes your multiline input more useful, although I guess you would need to decide if you'd recalculate all lines using a given variable if it's value changed ..