The Pending Home Sales Index climbed from an upwardly revised 104.6 in March to 110.9 in April, the association said.
The forward-looking economic indicator was 22.4 percent higher than April 2009.
"There were concerns that only a small pool of buyers were left to take advantage of the tax credit extension," association chief economist Lawrence Yun said. "But evidently the tax stimulus, combined with improved consumer confidence and low mortgage interest rates, are contributing to surging sales."
The federal tax credit for first-time buyers, which expired April 30, added 1 million buyers to the market, he said.
The Realtors group said the pending home sales index jumped 24.5 percent to 97.9 in April in the Northeast and rose 4.1 percent to 104.2 in the Midwest. In the South, the index dropped 0.6 percent to 123.9. In the West, the index rose 7.5 percent to 107.9.