Close to a quarter of all homeowners in the United States were considered "equity rich" due to low loan-to-value ratios, according to an analysis of home values in the third quarter of 2016.

ATTOM Data Solutions, owner of the real estate data company RealtyTrac, recently released its U.S. Home Equity and Underwater Report for the quarter. While a large number of homeowners had the potential to realize a major profit on their home's equity, more than 10 percent of homeowners were still struggling with seriously underwater mortgages.

Approximately 13.13 million U.S. homeowners had a loan-to-value ratio of 50 percent or lower. In this scenario, a homeowner's mortgage balance is no more than half of the fair market value of the property. This number was up by 2.6 million compared to the third quarter of 2015, representing 23.4 percent of all homeowners who financed the purchase of their residence.

"Close to one in every five U.S. homeowners with a mortgage is now equity rich thanks to a combination of rising home prices and lengthening homeownership tenures," said Daren Blomquist, senior vice president at ATTOM Data Solutions. "Median home prices increased on a year-over-year basis for the 18th consecutive quarter in Q3 2016, and homeowners who sold in the third quarter had owned their home an average of 7.94 years – a new high in our data and substantially higher than the average homeownership tenure of 4.26 years pre-recession. As homeowners stay in their homes longer before moving up, they are amassing more home equity wealth."

Homeowners in the West were the most likely to benefit from rising home values. Of the 88 metropolitan statistical areas with a population of at least 500,000 included in the study, San Jose had the highest share of equity rich homeowners at 55.7 percent. A total of 49.8 percent homeowners in San Francisco, 39.3 percent in Honolulu, and 38.2 percent in Los Angeles were equity rich.

Other large metropolitan statistical areas with a high percentage of equity rich homeowners included Pittsburgh (34.5 percent), Portland, Oregon (33.1 percent), San Diego (33 percent), Oxnard-Thousand Oaks-Ventura, California (32.7 percent), Seattle (31.5 percent), and Austin, Texas (31 percent).

In seven of these metro areas, the share of equity rich homeowners was up by more than 10 percentage points from the previous year. These cities included San Francisco and San Jose (both up 11.9 percentage points), Cape Coral-Fort Myers, Florida (up 11.5 percentage points), Portland and Denver, Colorado (both up 11.2 percent), and Austin and Seattle (both up 10.8 percentage points).

On the other end of the spectrum, approximately 6.06 million homeowners in the United States were considered to be seriously underwater on their mortgage. These homeowners were defined as having a loan-to-value ratio of 125 percent or more, or a mortgage balance at least 25 percent greater than the value of the property.

This total was down from a peak set in the second quarter of 2012, when close to 13 million homes were seriously underwater and accounted for 28.6 percent of all mortgaged residences. It was also a decrease of 854,000 properties from the third quarter of 2015. However, 10.8 percent of all mortgaged homes were still defined as being seriously underwater.

In seven of the 88 major metropolitan areas in the report, the share of seriously underwater homes stood at 20 percent or higher. Most of these cities were concentrated in Ohio, including Akron (24.2 percent), Cleveland (22.8 percent), Toledo (21.7 percent), and Dayton (20.2 percent).

Las Vegas had the highest share of seriously underwater homes at 25 percent. In both Detroit and Lakeland-Winter Haven, Florida, one in five mortgaged properties were seriously underwater.

While the national share of seriously underwater homes decreased, it was higher than the previous year in 21 of the 88 metro areas. These communities included Akron; Baton Rouge, Louisiana; Little Rock, Arkansas; McAllen-Edinburg-Mission, Texas; and Scranton-Wilkes-Barre-Hazelton, Pennsylvania.

In 17 of the 6,911 ZIP codes analyzed for the report, at least two-thirds of the mortgaged properties were seriously underwater. These ZIP codes included areas of Chicago, Detroit, Milwaukee, and St. Louis as well as parts of Columbus, Ohio; East Stroudsburg, Pennsylvania; and Trenton, New Jersey.

ATTOM Data Solutions bases its home equity reports on open loan and property value data. Its calculations on equity and loan-to-value ratios are also compared to data on foreclosures.