Rising home values in the United States helped shrink the number of properties worth considerably less than the amount owed on their mortgage in 2015, according to the real estate data company RealtyTrac. This analysis also found that a record number of properties in foreclosure have significant equity.

In its U.S. Home Equity and Underwater Report for the end of 2015, RealtyTrac determined that 6.44 million homes are seriously underwater. The report defines a seriously underwater residence as one where the loan amount on the property is at least 25 percent more than its estimated market value. An estimated 11.5 percent of all homes with a mortgage were estimated to be seriously underwater.

The share of seriously underwater homes has been falling steadily since the end of 2014. At that point, a total of 7.05 million mortgaged homes—12.7 percent of the total—fell into this category. While the share stayed at 12.7 percent at the end of the third quarter of 2015, the number of seriously underwater residences had fallen to 6.91 million.

These figures were significantly lower than the second quarter of 2012, when seriously underwater homes were most prevalent. At the end of that quarter, RealtyTrac determined that 28.6 percent of mortgaged properties in the United States—12.82 million in total—were seriously underwater on their loan.

"Over the past three-and-a-half years, the number of seriously underwater properties has been cut in half, but we continue to deal with a long tail of seriously underwater properties, and it will likely be another five years at least before most of those remaining underwater properties move into positive equity territory," said Daren Blomquist, vice president at RealtyTrac. "At the other end of the spectrum, the growing number of equity rich properties reflects a moribund move-up market and restrained leveraging of home equity by U.S. homeowners."

The report defines an equity rich property as one where the loan-to-value ratio is 50 percent or lower, meaning the homeowner has at least 50 percent equity in the residence. At the end of 2015, 12.62 million homes—22.5 percent of all residences with a mortgage—were considered to be equity rich.

This share was up from 19.2 percent at the end of the third quarter of 2015 and 20.3 percent at the end of 2014. The number of equity rich homes also rose, from 10.48 million at the end of the third quarter and 11.25 million at the end of 2014.

Seriously underwater homes were more likely to be inexpensive and have loans that began less than 10 years ago. Equity rich homes were generally owner-occupied, had been owned for a longer period of time, and were worth more than $1 million.

Sixty-three percent of all seriously underwater homes had a loan originating in 2008 or earlier, and 57 percent had been owned for a decade or less. Fifty-nine percent of these homes were owner-occupied.

One-third of homes valued at $100,000 or less were considered to be seriously underwater. By contrast, only 8.7 percent of the properties valued above $100,000 were considered to be seriously underwater.

Seventy-seven percent of equity rich homes were owner-occupied, and 62 percent had been owned for 10 years or more. Fifty-two percent had a loan that had been taken out in 2009 or later.

Nearly half of the equity rich properties with a mortgage—47 percent—were valued at $1 million or more. Among homes worth less than $1 million, 21.7 percent were equity rich.

Las Vegas, Nevada, had the highest share of seriously underwater homes among metropolitan statistical areas with at least 500,000 people, with 27.7 percent of mortgaged properties falling into this category. Florida and Ohio accounted for the next four markets with the largest share of seriously underwater homes, including Lakeland, Fla. (24.4 percent), Cleveland, Ohio (24.2 percent), Akron, Ohio (22.5 percent), and Orlando, Fla. (22.2 percent).

California had the markets with the lowest percentage of seriously underwater homes. The share stood at 1.8 percent in San Jose and 3.8 percent in San Francisco.

Other cities where seriously underwater homes were less common included Austin, Texas (3.9 percent), Portland, Oregon (4.2 percent), and Boston, Massachusetts (4.2 percent).

San Jose and San Francisco also had the highest percentage of equity rich homes at 53.7 percent and 47.6 percent, respectively. Other areas where equity rich properties were common included Honolulu, Hawaii (36.7 percent), Los Angeles, Calif. (35.8 percent), and Pittsburgh, Pennsylvania (35 percent).

Equity rich homes were least likely in Memphis, Tennessee, where only 11.4 percent of residential properties with a mortgage had at least 50 percent equity. Smaller shares were also observed in Dayton, Ohio (12.1 percent), Indianapolis, Indiana (12.4 percent), Las Vegas (13.1 percent), and Cleveland (13.3 percent).

Nearly half of all U.S. homes in some stage of foreclosure—49.7 percent—had equity. RealtyTrac says this is the highest share since the company began tracking this statistic in the third quarter of 2013. It was up from 34.6 percent at the end of 2014 and 43.3 percent at the end of the third quarter of 2015.

Denver, Colorado, had the largest share of foreclosed properties with equity at 89.6 percent. This was followed by Austin (88.8 percent), San Jose (87.5 percent), Pittsburgh (85.3 percent), and Nashville, Tenn. (83.6 percent).

Among all foreclosures at the end of 2015, 28.4 percent were seriously underwater. This share was at its lowest point since RealtyTrac began tracking this information in the second quarter of 2012, down from 34.6 percent at the end of 2014 and 33.4 percent at the end of the third quarter of 2015.

Las Vegas had the highest share of seriously underwater foreclosures, with 50.2 percent of these properties worth less than their outstanding mortgages. This city was followed by Chicago, Illinois (46.7 percent), Lakeland (46.1 percent), Cleveland (45.1 percent), and Deltona-Daytona Beach-Ormand Beach, Fla. (44.9 percent).

RealtyTrac used publicly recorded mortgage and deed data for the report, as well as an automated valuation model to determine the loan-to-value ratio. The report uses information from a database of more than 140 million residential properties in the United States.