More than 28 percent of U.S. homeowners with mortgages owed more than their properties were worth in the first quarter as values fell the most since 2008, Zillow Inc. said today.

Homeowners with negative equity increased from 22 percent a year earlier as home prices slumped 8.2 percent over the past 12 months, the Seattle-based company said. About 27 percent of homes with mortgages were ‘underwater