Calculating a running total in an Excel table is a little tricky, because it's not obvious how to build the formula with structured references. You can easily get the current row with the @ notation, but what about the first row in a column? You might be surprised that you can use INDEX for this.
This video shows how to setup VLOOKUP with a table, and how to use the MATCH function inside VLOOKUP to generate a dynamic column index. This makes it easy to refer to columns by name inside VLOOKUP, instead of hardcoding the column number. As a bonus, you can reorder the columns and the formula will keep working correctly.