Frank,
I guess you could say there's leverage, and then there's what he does. Like most of his other activities, he does leverage better than everyone else. Most people borrow money at a certain interest rate in hopes of using that money to get a higher rate of return, and thus turn a profit (while employing very little of their own capital in the process). I believe he does this sometimes, when he finds interest rates favorable (I read that he'll sometimes borrow money if rates are attractive even if he doesn't yet need it...that way if a rare buying opportunity comes along, his "gun" is loaded, and the "bullets" were cheap...)
A far greater source of leverage are Berkshire's insurance subsideries, like you said. They generate a great deal of premium income, from underwriting. Much of that is later required to pay claims made on the polices. But in the meantime, this "float" is free money for Berkshire - an interest free loan! Now that's what I call leverage!
As for high rates of return, (I think his long term return on investment is estimated in the low 20's) he uses that "borrowed" money to buy great companies at bargain prices. A company doesn't have to grow at 100% a year like Ascend to get it's stock to go up that much. A great business with decent growth can give you that same return if you can buy it really cheap. Buffett's just better than anyone at recognizing when great companies are cheap...
Anyway, that's how I see it in a nutshell... |