These cities have the most overleveraged mortgage holders in the U.S.

Willis, Texas has the most overleveraged mortgage borrowers in the country, according to a study of 2,530 cities conducted by WalletHub.

Overleveraged borrowers are more likely to default on their mortgage if they have any financial shocks like a loss of income.

"If you can comfortably afford the payments, then a very high loan-to-value ratio is probably fine," said Jonathan Halket, an assistant professor at Texas A&M University in a blog accompanying the report. "Relying on house price growth to accrue equity is a mistake."

WalletHub calculated the ratio of the median mortgage debt (based on TransUnion data from September 2020) to the median income. Next, it looked at the ratio between each city's median mortgage debt and its median home value.

Those two ratios were then translated to overall scores between 0 and 100. WalletHub's calculations are only for each city proper and only considers income related to work.

The national median overleverage score is just above 27. Willis, located 50 miles north of Houston, has a score of 66.57, with a mortgage debt-to-income ratio of 555% and a mortgage debt-to-house value ratio of 168%.

Bell Gardens, Calif., 10 miles south of downtown Los Angeles, actually had the highest mortgage debt-to-income ratio in the study, at 955%. But since it had a relatively low mortgage debt-to-house value ratio, at 63%, its overleveraged score is 62.57, ranking it third overall, behind Dumfries, Va.'s 66.49.

Austin, Texas, the city ranked by Zillow as the hottest market for 2021, had a mortgage debt-to-income ratio of 415%, but a mortgage debt-to-house value ratio of 64%. Phoenix, the second city on the Zillow list has a 31.41 score, and No. 3 Nashville, Tenn.'s score is 37.56.

New York, the most populous city in the nation, has a score of 42.7, while No. 2 Los Angeles has a 46.24 score with No. 3 Chicago at 28.19.

At the other end of the scale, the least overleveraged city is the New York City suburb of Bronxville, at 1.99; its mortgage debt-to-income ratio is 157% but the mortgage debt-to-house value ratio is 16%. Decatur, Ga., is next at 5.43 and Homosassa, Fla., 70 miles north of Tampa, was third at 5.69.