Sales of previously occupied homes took the largest monthly drop in more than 40 years last month, plunging far deeper than expected after lawmakers gave buyers extended time to use a tax credit.

The National Association of Realtors says sales fell 16.7 percent to a seasonally adjusted annual rate of 5.45 million in December, from an unchanged pace of 6.54 million in November. Sales had been expected to fall by about 10 percent, according to economists surveyed by Thomson Reuters.

Buyers were no longer scrambling to qualify for a tax credit of up to $8,000 for first-time homeowners. It had been due to expire on Nov. 30, but Congress extended the deadline until April 30.

The median sales price was $178,300, up 1.5 percent from a year earlier and the first yearly gain since August 2007.