At the end of the first quarter, 20.6% of homes with jumbo mortgages were underwater, meaning the owners owed more on the mortgage than the home was worth. That’s compared with 32.3% a year ago, according to real-estate website Zillow.com As the real-estate market rebounds, many luxury homeowners who just a few years ago had their heads underwater are now only ankle deep. More important, the level of negative equity has improved significantly for homeowners, said Stan Humphries, chief economist for Zillow. “Nationally most people in negative equity are in relatively shallow water, with less than 20% negative equity,” he said, meaning that borrowers’ loan-to-value percentage is less than 120%.