Think your 401(k) has suffered in the stock and bond market rout? Consider the Federal Reserve's recent woe: the U.S. central bank has lost at least $151 billion in the past seven weeks. And counting, Fortune reports.

Economists both inside and out of the Fed have long suspected the U.S. central bank would eventually lose money on the roughly $2.5 trillion in bonds it has bought since the financial crisis in an effort to stimulate the economy.