What is the function of an 'out-of-pocket maximum' in a health plan?

The out-of-pocket maximum is the most an insured will have to pay for covered, in-network services during a plan period through deductibles, copayments, and coinsurance combined. Once the insured's spending reaches this cap, the plan generally pays 100% of additional covered, in-network costs for the rest of the period (premiums do not count toward it, and out-of-network costs may not either). This limit protects the insured from catastrophic medical expenses. Understanding the out-of-pocket maximum — and how it differs from the deductible (the upfront amount before coverage begins) — is fundamental cost-sharing content on the health insurance exam.