I need some clarification on the calculation of margin interest. I understand that if I were to have a hypothethical portfolio of $10,000 and I bought $15,000 dollars worth of stock I would be charged interest on the $5,000 dollars borrowed to buy stock. My question is how this works on the short side. If I had the same $10,000 dollar portfolio and and bought $10,000 dollars of stock and SHORTED $5,000 dollars in stock would I be charged margin interest on the $5,000 worth of shorts? Is there a difference?