WASHINGTON (MarketWatch) – The number of new sales contracts on existing homes jumped a seasonally adjusted 6.3 percent in December as buyers took advantage of lower mortgage rates and falling prices, the National Association of Realtors reported today.

The pending home sales index rose 6.3 percent in December and is now up 2.1 percent compared with a year earlier.

The index is based on signed sales contracts, which usually occur a month or two before the sale is closed.