An out-of-pocket maximum is the limit on what you pay during the plan year for covered in-network essential health benefits under the plan's rules. After eligible spending reaches that limit, the plan generally pays 100% of covered in-network essential health benefits for the rest of the plan year.
What may count?
Deductibles, copayments, and coinsurance for covered services can count toward the limit. The specific plan documents determine how covered payments are applied and whether family-level limits operate separately from individual limits.
What generally does not count?
Monthly premiums usually do not count. Non-covered services, most out-of-network spending, and charges above the plan's allowed amount may not count toward the in-network out-of-pocket maximum. There are exceptions and separate protections for certain situations, so check the actual plan.
Why compare the limit?
The out-of-pocket maximum can help explain potential exposure for covered in-network care, but it is not a cap on every health-related expense. Compare it with premiums, deductibles, network participation, prescription coverage, and services you expect to use.
Official background: HealthCare.gov glossary.