Formulas' on Dynamic Range

Lets say I have a two columns, one with data, another with a simple function:
1 =A1
2 =B1+A2
3 =B2+A3
4 =B3+A4
5 =B4+A5


Now lets say I want to make column1 dynamic. How can I get the formulas in Column2 to also be dynamic? Other then stretching the formulas down to fill the entire column?


Basically I have a pivot table with a stock price and I want to make a cumulative line chart but the amount of data can differ depending on the stock.

Thanks so much!