Here’s a surprise everyone hates: an unexpected medical bill when you thought your insurance would cover everything.

Patients often face steep bills when they wind up with a provider who isn’t in their network. In-network doctors and facilities have an agreement with your health plan to offer contracted rates to members; your copayments and deductibles are likely lower with them.

You’ll pay a steep price for going outside that network.

“Out-of-network costs often don’t even go toward your deductible, or your deductible is so huge that it breaks the bank,” said Carolyn McClanahan, MD, director of financial planning at Life Planning Partners in Jacksonville, Florida, and a former physician.

One in 5 inpatient hospital admissions that start in the emergency room may lead to an unexpected bill, according to December 2016 research in Health Affairs, a health-care policy journal.

“In any in-facility service, whether you go through the emergency room or check in through the front door to stay for a procedure, that’s an opportunity for a surprise bill,” said Karen Pollitz, senior fellow, specializing in health reform and private insurance at the Kaiser Family Foundation.

“It’s likely a team of health professionals may participate in your treatment and you will have nothing to say about who those people are,” she said.

Expect a large bill if you see these physicians and experts out of network.