If I go long a stock and have sufficient cash in my account to fully fund the position, my broker charges me nothing because I have purchased and own the shares. But what happens if I short a stock? How much will my broker charge me assuming that there is always enough cash in my account to fully fund the position for as long as I'm short the stock. If there are borrowing costs, how do I determine them? (I use Interactive Brokers in case this question is broker specific.)