Combined March and April figures boosted sales to the highest level since May 2008, but still well below housing boom levels.
Sales are likely to slow in the next several months without the tax incentive, combined with constrained lending and slow job growth.
The rise in sales follows a 7.6 percent jump in existing home sales in April, announced Monday by the National Association of Realtors.
Sales were up in every region except the Northeast. Sales increased 31.6 percent in the Midwest, 21.7 percent in the West and 10.8 percent in the South.