NEW YORK (TheStreet) -- Watching the market's reaction to the Department of Labor's monthly jobs report can be more fun than the report itself. If, of course, you're into that sort of thing and you're not losing money because of the market's reaction.

Friday's jobs report was no different. The economy added 280,000 jobs in May, much higher than analysts' consensus of 226,000 and Goldman Sachs' estimate of 210,000. The result: Banking stocks jumped, with the KBW Bank Index gaining 1.7% and the S&P 500 Financials Index climbing 0.72%. The broader S&P 500 dipped 0.6%.

The reason for the gap between JPMorgan Chase (JPM), Bank of America (BAC), and Citigroup (C) and the rest of the market is simple: The monthly jobs report has been used as a barometer of when the Federal Reserve is likely to raise rates, a move about which the broader market has mixed feelings.

The mere act of a rate hike signals that the economy is performing well, which is good for consumption and business growth, but according to data compiled by S&P Capital IQ in February, the S&P 500 fell 11 out of 16 times in the three months after the first rate hike.

Banks are a different story: Low rates have compressed banks' net interest margin, a figure that gauges the profitability of lending cash deposited by their customers. They are unable to lend at a high rate, and with interest rates near zero since the financial crisis of 2008, it's not like they can pay any less on deposits.

In fact, net interest margin dropped to an average of 3.09 for the nation's largest banks in 2014 from a 10-year high of 3.89 in 2005, according to data analyzed by Bloomberg. Charlotte, N.C.-based Bank of America as well as JPMorgan and Citigroup, both based in New York, all saw lending profitability drop during that period.

Further, many of the other ways banks are able to earn money from consumer banking, such as fees, are increasingly under scrutiny in the post-recession era. A rate hike would suggest that banks could earn more from their lending business.

While some banks have been hesitant to provide targets for how a rate hike would play out, JPMorgan CFO Marianne Lake said in February that her New York-based company might see a $4.5 billion, or 20%, after-tax increase in net income by 2017 based on rate hikes alone.

Lake's analysis assumed a rate hike beginning in the second half of this year and rising to 2.25% by 2017. That may be a conservative estimate: A chart released in March showed Fed members estimated rates hovering around 3.1% by 2017.

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