It’s open enrollment season, the time each year when millions of American workers and retirees must choose a health plan, whether new or existing.

But picking health insurance can be a dizzying venture. Health plans have many moving parts — which may not come into focus at first glance. And each has financial implications for buyers.

“It is confusing, and people have no idea how much they could potentially have to pay,” said Carolyn McClanahan, a certified financial planner and founder of Life Planning Partners, based in Jacksonville, Florida. She is also a medical doctor.

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Making a mistake can be costly; consumers are generally locked into their health insurance for a year, with limited exception.

Here’s a guide to the major cost components of health insurance and how they may impact your bill.