A total of 9.7 million American homeowners have "underwater" mortgages, meaning they owe more on their home than it is currently worth, according to real estate analytics firm Zillow, Forbes.com reported. Homes in the lowest price tier are most affected, according to data released today by Zillow. Thirty percent of homes in the bottom price tier ($98,400 median price) are in negative equity, while 18 percent of homes in the middle tier ($163,400) and nearly 11 percent in the top tier ($306,700) are underwater, according to Zillow's Negative Equity Report. Overall, about 19 percent percent of homeowners were underwater during the first quarter of 2014. And more than one-third of all homeowners with a mortgage were "effectively" underwater, meaning they have less than 20 percent equity in their home. The Zillow report underscores a potential reason for the low prevalence of first-time home buyers in the market: Many owners of less expensive homes can't afford to sell.