Here's what happens to markets when Yellen speaks

Jewel Samad| AFP | Getty Images

Wednesday afternoon, traders will be parsing every word of the Federal Reserve's statement on interest rates and the news conference by Chief Janet Yellen for clues as to exactly when the central bank will increase its benchmark rate.

According to CNBC's Fed Survey, 92 percent of participants expect the central bank to begin raising rates this year, with the projection calling for a 0.5 percent increase.

Read MoreWall St sees rate hike in 3Q: Survey

"I will be surprised if the Fed will not begin to raise interest rates in September," said John De Clue, chief investment officer at U.S. Bank Wealth Management.

Below is historical performance of stock, bond, oil and currency markets on the day Yellen speaks.