One in five U.S. adults - an estimated 51 million people - will be contacted about medical bills by a collection agency in 2014, according to a study by NerdWallet Health.

Americans pay three times more in medical debt to collection agencies than they pay for credit card and bank debt combined, the study found.

Hospital billing errors result in overcharges of up to 26%, according to the study. Sixty-three percent of American adults say they receive medical bills that cost more than expected; 57% say they receive medical bills that confuse them; and 73% agree they could make better health decisions if they knew the cost of medical care before receiving it.

Between 2010 and 2013, U.S. households lost $2,300 in median income even as their health care expenses increased by $1,814. Out-of-pocket spending is expected to accelerate to a 5.5% annual growth rate by 2023 – double the growth of real GDP, according to the study.

In May 2013, NerdWallet Health reported that medical bankruptcy is the top cause of personal bankruptcy in the U.S. In the last year, there has been a surge of activity intended to lower consumer health expenses.

Most notably, the Affordable Care Act’s individual mandate and FICO score calculations have changed to decrease strain on those who hold medical debt.

NerdWallet used a survey conducted online in August by Harris Poll and reviewed publicly available public and private sector reports, including data from the U.S. Census Bureau, Milliman Medical Index and Centers for Medicare & Medicaid Services.

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