I just finished updating my comparison of broker margin rates. IB still offers (by far) the lowest margin rates, followed by OptionsHouse and TradeMonster.

After a several years of compiling this data on a regular basis, it still surprises me just how large a disparity there is between different online brokers. Brokers such as TradeStation, TD Ameritrade and ThinkOrSwim charge margin rates that are several multiples higher than other brokers. 

The lesson to be learned here is that it's worthwhile to shop around for a broker with a good mix of reasonable margin rates, low commissions, good execution and other factors that make a broker attractive.

ThinkorSwim just released a 7 minute video tutorial on Portfolio Margin. I've seen a few video overviews of PM and this one is probably the best I've seen so far. It's short, but the video presents the main concepts of Portfolio Margin and is reasonably accurate in its content. Kudos to TOS for their effort. 

I've updated the list of broker margin rates. A notable surprise was the substantial increase in TradeMonster's margin borrowing rates. I'm not sure exactly what their strategy is here (besides making more money that is), but such a significant change in the margin rate can't be good for Portfolio Margin investors.  

I've spent a lot of time talking about the margin rates offered by various on-line brokers and the impact it can have on a trading strategy. Unfortunately, I have yet to find a decent comparison of margin rates across various brokers. While a handful of sites compile this data they are almost always lacking in some critical way (updated infrequently or incomplete in their list of brokers). 

So, I've created a new page on The Margin Investor site with an updated comparison of broker margin rates. 

The chart below illustrates margin rates for a small brokerage account. It continues to surprise me just how how much variability there is between different brokers. 
See here for the full list.