http://individuals.interactivebrokers.com/en/accounts/fees/stocksPricing2.php?ib_entity=llc this is the following link to IB's rate. it says for the first 300,000 shares it costs you x, next 2,700,000 it cost you x, etc. like say in september I do 300,000 shares in october will I pay the rate for less than 300,000 or 300,000 to 2,700,000? how often does this update?