The end of Ben S. Bernanke's term as Federal Reserve chairman in January 2014 hasn't stopped investors from betting the central bank will hold the benchmark interest rate close to zero into the following year.

Bond-market measures from overnight index swaps indicate no increase in the federal funds rate until mid-2015, compared with the central bank's current view that the rate will probably stay low at least through late 2014. The gap between two- and five-year Treasury yields, which shrinks when traders expect benchmark rates to remain subdued, is more than 50 percent narrower than its average since 2008.

Bernanke has come under attack from Republican presidential candidate Mitt Romney, who said he won't reappoint the Fed chairman and criticized his policies as ineffective and a threat to price stability. That isn't impairing Bernanke's use of a forecast for the fed funds rate as a policy tool, said Joseph Gagnon, a former associate director at the Fed Board's Division of International Finance.