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Having health insurance shields you from the full brunt of medical expenses, but it's no guarantee that your costs will be low. Nevertheless, health-care bills still come as a surprise to many individuals who have insurance. Close to half of adults who bought their own coverage, along with 43 percent of those with insurance through their employer, said they were surprised by the high cost of their most recent health-care bill in the last year, according to a survey from Bankrate.com. The personal finance site polled 1,000 individuals in July. "For a lot of people who've had insurance for decades, there's a creeping sensation that more cost is being thrown onto them," said Taylor Tepper, an analyst at Bankrate.com. Here's why you can still pay massive bills despite having insurance coverage.

Cost sharing

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You're not just seeing things: Consumers are paying more money in the form of higher premiums, deductibles and additional expenses. Last year, annual family premiums for health insurance through the workplace rose to $18,764, an increase of 3 percent from 2016, according to the Kaiser Family Foundation. Of that amount, on average, workers contributed $5,714 to these family plans, accounting for their share of the premium, Kaiser found.

High deductibles

Though low-premium insurance options are available in the form of high-deductible health plans, consumers are paying a sizeable amount of expenses before their coverage kicks in. The IRS defines a high-deductible health plan as one that has a deductible of at least $1,350 for individual coverage or $2,700 for family coverage. These plans often work alongside a health savings account, which customers can use to sock away cash on pretax or tax-deductible basis. This money grows free of taxes and you can withdraw from it on a tax-free basis as long as you're using your cash to pay qualified medical expenses.

Other costs

These expenses only tell part of the story. Consumers are also coughing up money for copayments — the amount of money you pay each time you visit a doctor or buy a prescription drug. In 2016, employees paid an average of $140 toward copays, down from $225 in 2006, the Kaiser Family Foundation found. See below for details.

That's because insurance companies and plans are using other levers to share expenses with employees, namely coinsurance, which takes effect after employees hit their annual deductible. At that point, the insurer will cover a percentage of the cost of service, while the employee pays the rest. On average, workers were responsible for 19 percent of the cost of a hospital admission in 2017, according to the Kaiser Family Foundation. In comparison, the average copayment for a hospital visit is $336 per admission.

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