For a running balance or running total such as the following:
Column Name: A B C D (Where C = Balance and D = Running Balance)
Row 1: x y $50 =$C1
Row 2: y z $30 =$C2 + $D1
Row 3: a b $20 =$C3 + $D2
From here, select drag D3 and pull it down to the bottom. Excel will be
smart enough to increment the row numbers. It will keep the column names
locked because of the ($).