WASHINGTON — Federal Reserve Board Chair Janet Yellen on Wednesday suggested policymakers could begin to lift interest rates roughly six months after the central bank winds down its bond buying program this fall.

Speaking at her first press conference, the central banker offered the most concrete time frame on when the Federal Open Market Committee could begin to raise the benchmark rate, which has sat at a range of zero and 0.25% since December 2008.

The Fed has consistently projected it would maintain the target range for the federal funds rate for a "considerable time" after the asset purchases ended, especially if inflation continued to run below the central bank's 2% inflation target.

On Wednesday, policymakers appeared on course to end its quantitative easing program later this fall following its decision to again shrink its monthly pace of purchases of mortgage and Treasury bonds. The FOMC agreed starting in April to reduce its purchases to $25 billion and $30 billion of mortgage-backed securities and longer-term Treasury securities, respectively.

Fed officials have been reluctant to quantify specifically what a "considerable time" would entail.

"This is the kind of term [that] is hard to define, but… it probably means something on the order of around six months or that type of thing," Yellen told reporters following a two-day FOMC meeting.

That would appear to indicate the Fed would plan to start raising rates roughly a year from now if it kept to Yellen's timeline.

Her guidance on the issue sparked an immediate sell-off on Wall Street. The Dow Jones Industrial Average shed 114 points, or 0.7%, to 16222. The S&P 500 index slipped 11 points, or 0.6%, to 1860 and the Nasdaq Composite Index slipped 26 points, or 0.6%, to 4308.

Still, she added nuance to her answer by suggesting any rate hike would be dependent on current economic conditions.

"We need to see where the labor market is, how close are we to our full employment goal," said Yellen. "This will be a complicated assessment not just based on a single statistic. And how rapidly are we moving toward it? Are we really close and moving fast? Or are we getting closer, but moving slowly?"

Adding to the complexity, policymakers also agreed at their March meeting to revise their forward guidance, an instrument central bankers have used to provide additional details to the market on the timing of their decision to lift interest rates.

Fed officials dropped mention of a 6.5% jobless rate as a target threshold that would need to be surpassed before considering raising short-term interest rates. As the unemployment rate continues to fall, Fed officials have suggested that it may be time for the central bank to change its guidance.

"Markets want to know, the public wants to understand beyond that threshold how will we decide what to do? So the purpose of this change is simply to provide more information that we have in the past," said Yellen.

Instead, the Fed will base its decision to lift rates on a wide range of information, including labor market conditions, inflation pressures and inflation expectations and reading on financial developments.

"We've tried to give a general formulation of what we'll be looking at, which is how far are we, how large are the shortfalls in achieving our goals, and how fast can we expect progress to be? That will be the main factors we'll be looking at," said Yellen.

During her first press conference, Yellen stuck almost entirely to monetary policy, but briefly mentioned ongoing work on bank regulatory matters.

When asked how she differs from her predecessor, Ben Bernanke, Yellen indicated she largely planned to continue his agenda.

"Strengthening the financial system is a work in progress, and he made large inroads in strengthening the financial system," she said. "I'd just say, there is more work to be done. I have a long to-do list. It is a high priority to see further work done in addressing too big to fail… And we want to be extremely cognizant of emerging threats to the financial system."

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