Four terms show up on nearly every health insurance bill, and mixing them up is one of the most common ways people misjudge what a plan actually costs. Here's what each one actually means. * Your premium is the amount you pay just to keep your insurance active — typically monthly, and you pay it whether or not you go to the doctor at all that month. Missing premium payments can get your coverage canceled entirely, regardless of how healthy you've been. * Your deductible is the amount you have to spend on covered care before your plan starts paying its share, aside from certain preventive services that are often covered from day one. * A copay is a flat, fixed dollar amount you pay at the time of service — say, $30 every time you see your primary care doctor, regardless of what that visit actually cost the insurer. Copays are simple because the number doesn't change based on the size of the bill. * Coinsurance is different from a copay: it's a percentage, not a flat fee, and it only kicks in after you've met your deductible. If your coinsurance is 20% and a covered service costs $1,000, you pay $200 and your insurer covers the remaining $800. * Put together, a typical year of using your insurance looks like this: you pay your premium every month regardless, then pay 100% of costs (except preventive care) until you hit your deductible, then split costs through coinsurance or copays until you reach your plan's out-of-pocket maximum, after which your insurer covers 100% of covered costs for the rest of the year.