Premium-free Part A eligibility is based on earning Medicare work credits through payroll taxes. Forty quarters of work (about 10 years) qualifies you for premium-free Part A, and you can also qualify if you’re the spouse or widow(er) of someone who has earned those credits. Age alone isn’t the trigger, and you don’t have to enroll in Part B to receive Part A. A government job isn’t a requirement either; eligibility comes from your own or your spouse’s work credits.

Coinsurance in Medicare is the cost-sharing that kicks in after you’ve paid the deductible for that service. Once the deductible has been met, you’re responsible for a percentage of the covered costs as coinsurance (for Part B most commonly 20%, while Part A has per-day coinsurance after the hospital deductible for extended stays). It isn’t a fixed monthly payment, and it isn’t paid before the deductible or limited to private plans—coinsurance is the standard cost-sharing you pay after meeting the deductible for Medicare-covered services.

The key idea is understanding how Part D plans organize medicines and what you pay. A formulary is the plan’s official list of prescription drugs that it covers. Each drug on that list is assigned to a tier, and those tiers determine your cost-sharing. Lower tiers, which often include generic or preferred options, usually come with lower copays or coinsurance. Higher tiers cover more expensive options like brand-name drugs or specialty medications and carry higher out-of-pocket costs. The exact amounts depend on your plan, and some drugs on the formulary may still require additional rules like prior authorization or step therapy. The other choices describe things like pharmacy hours, prescription limits, or requiring a specialist, which aren’t what a formulary or drug tiers are about.

In Medicare Part D, the donut hole represents a coverage gap where your out-of-pocket costs rise. After you and your plan have spent a certain amount on covered drugs in a year, you enter this phase, and you end up paying more for your prescriptions until you reach catastrophic coverage. It’s about higher cost sharing, not a reset of the deductible, and it applies to both brand-name and generic drugs, not just brand-name. Once you hit the catastrophic threshold, your costs drop back to the small copays or coinsurance for the rest of the year.