What is the deductible vs. copay vs. coinsurance vs. out-of-pocket maximum?

Four cost components in most modern plans. Premium: monthly amount you pay to keep the plan active, regardless of whether you use it. Deductible: annual amount you pay out of pocket before the plan starts paying for non-preventive services (preventive care is free under ACA). Copay: a fixed dollar amount per service after the deductible (e.g., $25 per primary care visit). Coinsurance: a percentage of cost you pay after the deductible (e.g., 20% of an MRI). Out-of-pocket maximum (OOPM): the most you'll pay in a year for in-network covered services — once you hit it, the plan pays 100%. The OOPM never includes your premium or services the plan doesn't cover. Key intuition: high-deductible plans have lower premiums but higher up-front costs; low-deductible plans have higher premiums but predictable costs.