American homeowners have been making strong gains on improving home equity in the past year, according to the real estate analytics company CoreLogic. The typical homeowner gained nearly $13,000 in equity in the past year, and the aggregate amount of homeowner equity more than doubled in the past five years.

The Homeowner Equity Insights report for the second quarter of 2017 determined that homeowners who are currently paying a mortgage on their residence gained $403 billion in equity over the first quarter of the year and $766.1 billion since the second quarter of 2016. This marked a year-over-year increase of 10.6 percent.

Total homeowner equality was up $4.2 trillion from the second quarter of 2012, reaching $8 trillion in the second quarter of 2017. A total of 94.6 percent of mortgaged properties had equity, up from 93.9 percent in the previous quarter and 92.9 percent in the second quarter of 2016.

"Over the last 12 months, approximately 750,000 borrowers achieved positive equity," said Frank Nothaft, chief economist at CoreLogic. "This means that mortgage risk continues to decline and, given the continued strength in home prices, CoreLogic expects home equity to rise steadily over the next year."

The average homeowner saw a year-over-year gain of $12,987. The booming markets on the West Coast showed the strongest growth, with average year-over-year equity gains of $40,379 in Washington, $33,834 in Hawaii, $30,022 in California, and $27,124 in Utah.

Among the 43 states with available data, only two showed a decline in equity growth. Alaska homes lost an average of $1,175 from the previous year. Equity in Delaware was relatively unchanged, losing an average of only $76.

Connecticut had an average year-over-year equity gain of $1,840. In Rhode Island, the average homeowner saw a $15,536 increase in equity.

A total of 2.8 million homes, or 5.4 percent of all mortgaged properties, had negative equity. In these cases, the outstanding mortgage balance was greater than the value of the home. The number of homes with negative equity was down 10 percent compared to the previous quarter and 21.9 percent compared to the second quarter of 2016. It was also down nearly 80 percent from the fourth quarter of 2009, when the negative equity share peaked at 26 percent.

The total value of negative equity among mortgaged U.S. properties stood at $284.4 billion at the end of the second quarter of 2017. This was up $200 million, or 0.1 percent, from the previous quarter. However, it was also a small decrease—$700 million, or 0.2 percent—from the second quarter of 2016.

Nevada continued to have the greatest share of underwater homes, with 10.6 percent of mortgaged properties worth less than the loan balance. However, it also had the largest decrease in negative equity, which fell 4.8 percentage points from the previous year. The negative equity share stood at 10 percent in Florida and 9.6 percent in Illinois.

Texas had the lowest negative equity share, with only 1.5 percent of the state's properties having values lower than the outstanding mortgage balance. A total of 1.6 percent of mortgaged properties in Utah, 1.7 percent in Washington, and 1.8 percent in Colorado, Hawaii, and Oregon were underwater.

In both Connecticut and Rhode Island, 8.6 percent of mortgaged homes had negative equity. This was an improvement from both the previous quarter (when the negative equity share was 9.9 percent in Connecticut and 9.4 percent in Rhode Island) and the previous year (when 10.3 percent of Connecticut homes and 11.3 percent of Rhode Island homes were underwater).

New York was the only state that didn't see some improvement in negative equity from the previous year. A total of 5.1 percent of mortgaged properties in the state were underwater, up 0.3 percentage points.

The Homeowner Equity Insights reports from CoreLogic focus on mortgaged properties in the United States, not those where the homeowner owns the residence outright. According to the 2016 American Community Survey from the U.S. Census Bureau, about 63 percent of U.S. homeowners have a mortgage.

CoreLogic's equity reports have consistently given a lower negative equity share than RealtyTrac, another real estate analytics company. In its report for the second quarter of 2017, RealtyTrac concluded that 5.4 million homes, or 9.5 percent of mortgaged U.S. properties, were "seriously underwater" since their loan-to-value ratio was at least 125 percent.