Here's an example not touching options or futures then:
I could have $1000 cash, sell $2000 worth of stock short, buy $3000 worth of stock long, and end up with a $0 cash balance, and I would not be borrowing anything?
I'm not suggesting that I would actually like to do that.
I have a margin account with Interactive Brokers. Is there any number in the platform or website that indicates how much I'm borrowing from them? How can I check myself? Is there a simple balance number I'm missing somewhere?
Let's keep things simple and say I have an USD based account, and am...