Is a peak coming in this key market metric?

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Recently everyone has been talking about margin debt on the New York Stock Exchange.

Margin debt is the dollar value of securities purchased by borrowing against a client's account and it carries an interest rate, which changes daily. That number recently topped $400 billion, higher even than the 2007 peak. It's been cited as a sign of confidence in this bull market but bears say its ascent suggests the end of the bull market is near.

The concern is that, as investors leverage their accounts and push the stock market higher, risks also increase. When the stock market capitulates, for those who can remember, margin calls happen every day and investors are forced to deleverage. Margin calls and forced selling are also often signs of a market bottom, but what can we use to identify a market top given these margin levels?

The first thing we need to do is to compare margin debt to credit balances. The ratio of margin to credit balances is less than it was during the Internet bubble but margin debt is still substantially higher than it was in 2000. During the Internet bubble, the ratio between margin balances and credit was almost 5 to 1, which was ridiculous, but we are not in or likely to be in that territory in this economy.

(Read more: Playing with fire? Margin debt most since crisis)

What is more interesting is the peak in margin debt that occurred in 2007. Credit balances increased proportionally to the margin debt going into that peak. In typical conditions, we would expect credit balances to increase when margin-debt levels increase and that is exactly what happened in 2007. The concern is that this relationship does not exist in our current environment.

Right now, margin debt is increasing while credit balances are flat-lining. Therefore, investors are assuming more risk and leveraging their portfolios much more without increasing their credit balances.

(Read more: Marc Faber: We're in a 'massive speculation bubble')

In my research, I discovered that the changes in margin debt since the credit crisis have been directly aligned with Federal Reserve policy decisions. The most interesting divergence coincides with the beginning of the Fed's third round of quantitative easing, or bond buying, which began last September. Exponential margin expansion occurred on the heels of this program's initiation, without increases in credit balances.

If nothing more, this observation tells us that when deleveraging comes, it will be much more violent than what we have seen in the past. The spreads between credit and margin are far too wide, and although proportionally not as disparaging as during the Internet bubble, the risks are quite clear.

(Read more: Stocks are 'very overpriced' — and so what if they are?)

Changes in margin debt can also be used to identify market declines before they happen, because smart money typically begins to deleverage before market declines actually happen. In my definition, smart money is the market as a whole, not just one investor or a group of investors, but smart money is the entire market and the market knows best. If you make a comparison of the changes that happened to the market after a peak in margin debt, you see that those peaks were in 2000, 2007, and 2011. Peaks in margin debt are often a precursor to major market decline.

Since the credit crisis, margin-debt levels have moved in parity with stimulus programs and the expectations thereof. Expectations may play a key role in the peak in margin debt that seems inevitably on the horizon.

— By Thomas H. Kee, Jr.

Thomas H. Kee, Jr. is president and CEO of Stock Traders Daily and founder of The Investment Rate. Follow him on Twitter @marketcycles.