Deductible — the threshold
Your deductible is what you pay out of pocket before the plan starts sharing most costs. Preventive care (annual physicals, screening colonoscopy, many vaccines) is usually exempt by law. Family plans typically have an individual deductible and a higher family deductible — and may be either embedded (one person can hit theirs and start getting coverage) or aggregate (the whole family deductible must be met first).
Copay vs coinsurance
A copay is a flat dollar amount ($25 for a primary care visit). Coinsurance is a percentage of the allowed charge after the deductible (you pay 20%, plan pays 80%). Some plans use copays for office visits and coinsurance for imaging, surgery, and hospitalizations.
Out-of-pocket maximum — the ceiling
Once your deductible + copays + coinsurance hit your annual OOP max, the plan pays 100% of allowed in-network charges for the rest of the plan year. Premiums, out-of-network charges, and non-covered services don't count toward this ceiling.
Worked example
$2,000 deductible, 20% coinsurance, $8,000 OOP max. You have outpatient surgery with $30,000 allowed charges. You pay the first $2,000 (deductible), then 20% of the next $28,000 = $5,600 — but only up to your $8,000 cap. Total you owe: $6,000 left after deductible, then nothing else for the year on in-network covered care.
Strategy
If you've already met your deductible mid-year, schedule other elective care before the plan year resets. If you're enrolled in an HSA-eligible HDHP, your contributions reduce taxable income and can cover deductible expenses tax-free.