Coinsurance

Coinsurance is the percentage of the allowed amount you pay after your deductible is met, up until you hit your out-of-pocket maximum. If your plan is "80/20 after deductible," the plan pays 80% and you pay 20% of every allowed charge until you cap out.

Here's where it gets real. Say you meet your $3,000 deductible in March, then need outpatient surgery in June with a $22,000 allowed amount. At 20% coinsurance, that's $4,400 out of your pocket on top of the deductible you already paid — total $7,400 for one procedure. That's why the out-of-pocket maximum matters so much: it's the ceiling that stops coinsurance from bleeding indefinitely. Self-funded employers set the coinsurance split in their plan document; fully-insured plans inherit whatever the carrier filed. Some employers use lower coinsurance (say 90/10) at designated Centers of Excellence to steer members toward higher-quality facilities.

The takeaway: coinsurance is where a "good" plan and a painful year diverge. Always run the worst-case math — deductible + coinsurance up to out-of-pocket max — before choosing a plan at open enrollment.