In 2017, one million American homeowners rode rising home prices into positive equity territory.

Negative equity—commonly referred to as being “underwater”—is when a homeowner owes more on a mortgage than the mortgaged property is worth.

According to a new report from real estate data analysis firm CoreLogic, just 3.17 million U.S. homes (6.2 percent) remain in negative equity. This is down from an all-time high of 26 percent in 2009, and if home prices rise another 5 percent, another 600,000 homes would re-emerge into positive territory.

Equity is the difference between how much your home is worth and how much you owe on your mortgage. Through mortgage payments and home appreciation, equity grows.

And building equity is a critical part of creating lifelong financial stability.

Since the home pricing dip of 2011, Americans have more than doubled their home equity to over $12 trillion. Even so, an Urban Institute study says some $11.3 trillion of that equity is “untapped.”

Short of selling and buying a less expensive home, homeowners can leverage home equity for a refinance to take advantage of more favorable loan terms.

Borrowers can also use equity as collateral for a home equity loan or home equity line of credit.

In an age when current generations—starting with the baby boomers—can no longer rely on pensions, and traditional savings plans can be vulnerable or underfunded, home equity is becoming more important than ever to those entering retirement. And many older homeowners are using their equity to obtain a Home Equity Conversion Mortgage (more commonly known as a reverse mortgage).

Home value doesn’t always go up. Financial recession and other factors can always cause an equity decrease. However, over the long term, real estate tends to increase in value.