The Seattle market’s home prices leapt 1.9 percent in July over the previous month and 12.5 percent over the past 12 months, according to the closely watched S&P/Case-Shiller 20-city home-price index.

Seattle, Tampa, Fla., and Washington, D.C., were the only three metro areas that saw monthly price gains accelerate from June to July.

The average price for existing single-family homes in King, Snohomish and Pierce counties, as measured by the Case-Shiller index, was still about 18 percent off the 2007 peak.

The 20-city index closely mirrored Seattle’s price gain: It rose 1.8 percent over June and 12.4 percent over the past 12 months. Through July, the average U.S. home price was back to spring 2004 levels, but still 21 percent below the pre-recession peak.

The increase in mortgage rates since May may be affecting the growth in home prices, S&P officials said.

“More cities are experiencing slow gains each month than the previous month, suggesting that the rate of increase may have peaked,” said David Blitzer, chairman of S&P’s index committee.

The Federal Reserve’s announcement last week that it will continue its bond-buying program at current levels “may have only a limited, though favorable, impact on housing,” he said.

Among the 20 metro areas covered by the index, Chicago saw the biggest monthly gain, jumping 3.2 percent in July, duplicating the market’s gain in June. Over the past 12 months, Las Vegas led all 20 cities, with a 27.5 percent increase in the average price.

San Francisco posted its highest year-over-year price gain since March 2001, with a 24.8 percent jump in the average price over the past 12 months, according to S&P.

The index measures the average price change in existing single-family homes that sold during a three-month period and did not undergo substantial remodeling since the home’s previous sale. Homes owned for less than six months are excluded.

Meanwhile, foreclosures on Seattle-area homes with mortgages shrank in July, reported CoreLogic.

The rate of foreclosures in the Seattle-Bellevue-Everett area was 1.81 percent, down from 2.31 percent a year ago, and was lower than the national rate of 2.43 percent, according to CoreLogic.

About 4.7 percent of mortgages locally were delinquent by 90 days or more, down from 6.68 percent in July 2012, CoreLogic said. Nationally, 5.44 percent of mortgages were delinquent.

Sanjay Bhatt: 206-464-3103 or sbhatt@seattletimes.com On Twitter @sbhatt