The Federal Reserve's announcement that it is unlikely to raise its benchmark interest rate until late 2014 is simply its "best guess," Ben Bernanke said Wednesday.
The Fed chairman made clear during a news conference Wednesday that the decision to leave interest rates unchanged for three more years was not ironclad.
The central bank's ability to forecast that far out is limited, Bernanke says, and the Fed could adjust the timetable for when it will raise rates if economic conditions change.
Still, he said the U.S. economy remains weak and all signs suggest the Fed won't change its record-low rate for another three years.
"We have to make a best guess," Bernanke said after the Fed concluded its two-day policy meeting. "Unless there is a substantial strengthening of the economy in the near term, I would think that it's a pretty good guess that we will be keeping rates low for some time from now."
The central bank has kept its key rate at a record low near zero for three years.
Bernanke also said the Fed has not ruled out bolder steps to boost economic growth, such as a third round of bond purchases.
"If inflation is going to remain below target for an extended period and unemployment progress is very slow ... there is a case for additional policy action," he said.
"I would not say we are out of ammunition. We still have tools."
Prior to the news conference, the Fed slightly reduced its outlook for U.S. economic growth this year. It forecasts the economy to grow between 2.2 percent and 2.7 percent in 2012, according to its updated economic forecasts. That's down from November's forecast of between 2.5 percent and 2.9 percent.
Many economists expect Europe will suffer a recession this year, which will slow U.S. growth.
Still, the Fed said it expects unemployment to fall as low as 8.2 percent. That's an improvement from November's forecast of 8.5 percent. The unemployment rate fell to 8.5 percent in December after the sixth straight month of solid hiring.
Inflation has been relatively tame and the Fed doesn't see that changing over the next three years.
The Fed's policies have made Bernanke a popular target for Republican presidential hopefuls. Several have criticized Bernanke for raising the risk of higher inflation.
Bernanke refused to answer a question asking whether he would resign if one of his critics wins the November election.
"I'm not going to get involved in political rhetoric," Bernanke said. "I have a job to do and as long as I'm here I will do everything I can to help the Federal Reserve. ... That's my answer."