The rush to buy before the tax credit expired boosted prices in many major metropolitan housing markets, according to Standard & Poor’s Case-Shiller home price indices released Tuesday. Eighteen of 20 cities tracked by Case Shiller posted increases in home prices in April, boosting the 10-city composite by 0.7% and the 20-city composite by 0.8% on a monthly basis.

Year-over-year, the 10-city composite is up 4.6% compared to April 2009, and the 20-city index recorded a 3.8% gain.

The 10-city composite index includes Boston, Chicago, Denver, Las Vegas, Los Angeles, Miami, New York, San Diego, San Francisco, and Washington. The 20-city composite covers those same 10 cities plus Atlanta, Charlotte, Cleveland, Dallas, Detroit, Minneapolis, Phoenix; Portland, Ore.; Seattle, and Tampa.

The big winners among these major markets? Washington (up 2.4% on a monthly basis), San Francisco (up 2.2%), and Dallas (up 2.0%). Miami and New York posted the only negative monthly numbers among the 20, with declines of 0.8% and 0.3%, respectively.

Index watchers attributed the pricing improvements to the tax credit that required buyers to sign a contract no later than April 30, just as it has boosted other housing numbers. “The tax credit pumped up demand through April and led to a surge in new and existing home sales, and a ramping up in housing starts,” said Patrick Newport, U.S. economist for IHS Global Insight in Lexington, Mass., who raised the question on many people’s minds. “With the credit now behind us, the housing numbers are taking a beating. What does this imply for the Case-Shiller indices?”

Unfortunately for builders, economists expect housing to wobble in the months ahead. “Other housing data confirm the large impact, and likely near-future pullback, of the federal program,” noted David M. Blitzer, chair of the index committee at Standard & Poor’s. “Recently released data for May 2010 show sharp declines in existing and new home sales and housing starts. Inventory data and foreclosure activity have not shown any signs of improvement. Consistent and sustained boosts to economic growth from housing may have to wait to next year.”

Newport sounded even more bearish. “In our view, the housing glut and foreclosures will drive the national Case-Shiller index down another 6% to 8%, with prices bottoming in 2011,” he said.

Both the Case-Shiller and Federal Housing Finance Agency indices track home values, but they are calculated differently. Case-Shiller focuses on the 20 largest metro housing markets and includes homes purchased with jumbo loans, which often results in more dramatic home price changes than the FHFA index. FHFA’s figures are based on the purchase prices of homes with loans owned or guaranteed by government-sponsored enterprises (GSE) Freddie Mac and Fannie Mae in all 50 states.

Alison Rice is senior editor, online, at BUILDER magazine.

Learn more about markets featured in this article: Miami, FL, Dallas, TX, San Francisco, CA, Washington, DC, Atlanta, GA.