newbie to spreadsheets

I hope this is the right place to post, if not, I do apologize. I am trying to teach myself how to do a spreadsheet. As a practice and also to keep track of things, I came up with a simple one that actually works.
the columns are DATE CHECK# AMOUNT BALANCE. To calculate the balance each time an amount is entered I have for a formula =SUM(D3-C4)

However, each time I enter an amount in the next row, I have to retype the formula in the balance so the next one would be =SUM(D4-C5)

My question is, Is there a way of making a formula for the BALANCE column to always calculate so I don't have to always put the formula in? So far, it's been fun playing around with spread sheet but I'm getting frustrated with this one.

Any help is appreciated.