[LearnedfromTV]

I think the proper way to think of investing "rake" is as a percentage of purchase size, adjusted for turnover. If you invest with a $7 commission and make $7000 purchases on average, you are paying a 0.10% expense fee per purchase. If your average holding period is one year, then you are spending .10% of your investment on transaction fees a year. If your average holding period is 1 week, you are spending .10*52 = 5.2% of your investment on transaction fees per year.

The average size of your purchases is determined by the amount you have to invest and the average number of stocks you will hold. Holding 10 stocks in a 10K portfolio and turning them over weekly, your yearly expense ratio would be 7/1000*52 = 35%. Maybe you should invest in Ameritrade to get some rakeback.

Edit: Two poker rake analogies apply. Higher stakes = rake is lower as a percentage. Play fewer hands, rake is lower as a percentage of bankroll because you put money in the pot less frequently.

Higher stakes = larger purchases/larger investment bankroll. Playing fewer hands = less turnover.