Please Help Me With My Stock Portfolio Spreadsheet

[TeachMeExcelPlease]

Hi, I am slowly trying to learn Excel and my recent project has been to create a stock tracker that calculates every trade and how much I made/lost, my account balance, etc. I am starting with $1000 and trying to see how long it takes to double my account.

The spreadsheet is nearly complete but there's one column I can't figure out. I'd like to track how much available money I have to invest at any given time. I have my present account value in cell (M3). I have another column (G) which contains the total cost of that particular trade. Finally, I have a column (E) which is where I put the selling price once I've exited the trade.

What I'd like to do is subtract my total account value - the cost of all the stocks I haven't yet sold.. So, M3 - the total cost (G) of any cell that doesn't have anything in column E.

I hope this makes sense. I've added a screenshot of my spreadsheet in case that helps. If I am not calculating this formula correctly to give me how much I have to invest at any given moment, please let me know. I'm terrible with numbers.

Thanks in advance!!

 

[TeachMeExcelPlease]

Edit -- it's saying my screenshot is to large to upload. I hope I made sense in my post above. Thanks again.