The index, which has also posted gains for 10 of the past 11 months, rose by 0.5 percent in November after a gain of 0.4 percent in October and 1.6 percent in September.
The index climbed to 108.3 the Conference Board said.
The index uses 2004 as a base year, assigning it the value of 100 to provide a reference point for comparisons.
The Coincident Economic Index, which measures current business conditions, also rose, climbing 0.2 percent in November to 105.7.
The steady climb suggests "the economy will continue expanding and its pace could even pick up moderately in the first half of 2014," Conference Board Chief Economist Bart van Ark said.
"Widespread strength from production and job growth, along with sustained support from monetary policy, will add fuel to the recovery. Productivity, however, will remain the Achilles' heel of Britain's long-term growth performance, as reflected in the Conference Board's latest release of productivity estimates," he said.
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