The tax reform plan in Congress helped push the Federal Reserve to raise its growth expectations for next year but wasn't the only factor, Fed Chair Janet Yellen said Wednesday.

Speaking to reporters following this week's Federal Open Market Committee policy meeting, Yellen said the current bill's move to cut corporate and personal rates will be positive for U.S. gross domestic product.

The Fed boosted its estimate for 2018 GDP from 2.1 percent in September to 2.5 percent at this week's meeting.

"My colleagues and I are in line with the general expectation among most economists that the type of tax changes that are likely to be enacted would tend to provide some modest lift to GDP growth in the coming years," Yellen said during her final news conference as Fed chair.

However, she said that other factors are at play as well. She also noted that committee members have been factoring in tax reform to their GDP projections all year, so the latest boost shouldn't be read as driven wholly by the tax cuts.

"There are many factors that affect those projections, and changes in tax policy, that's only one of a number of factors, including incoming data that is to some extent also the outlook for growth and inflation," Yellen added.

The FOMC decided to hike the Fed's target rate a quarter point to a range of 1.25 percent to 1.5 percent.

Yellen said expectations for growth, particularly in the labor market, factored into the Fed's decision to increase the target range.

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