Quote from JackR:
IB's commission rate goes down as your volume goes up. You start every month at the high rate and decrement down every time you hit the next volume step. This is the way they work it in the futures commission structure.
IB commission structure is applied to the various exchange and regulatory fees and rebates.
Here is the IB commission portion, all else is constant:
<=300,000 Shares $0.0035
300,001-3,000,000 Shares $0.002
3,000,001-20,000,000 Shares $0.0015
>20,000,001 Shares $0.001
There is an overiding minimum of $0.70 per trade if you don't do enough size in an individual order.
If you were to do 3 million shares your average commission would be .00215 per share. Depending on where and how you trade you could lower that by gaining liquidity rebates.
Jack