Medicare Coverage Gaps and What They Mean for You

Medicare coverage gaps are specific situations where the program stops paying — or never paid — leaving beneficiaries responsible for costs that can reach thousands of dollars per benefit period. This page explains the primary gaps built into Original Medicare, how they function mechanically, common scenarios where they appear, and the decision points beneficiaries face when choosing how to address them. Understanding these gaps is foundational to making informed choices about supplemental coverage options and overall Medicare planning.

Definition and scope

A Medicare coverage gap is any point in the benefit structure where the program either imposes no upper limit on cost-sharing, excludes a category of care entirely, or provides only partial reimbursement after certain thresholds. The term applies to two distinct phenomena that are frequently conflated: structural cost-sharing gaps within Parts A and B, and the Part D prescription drug coverage gap (historically called the "donut hole").

Structural gaps in Medicare Part A and Medicare Part B include:

• No out-of-pocket maximum in Original Medicare. Unlike most private insurance, Original Medicare imposes no annual cap on combined cost-sharing. A beneficiary with a catastrophic illness can owe unlimited amounts through coinsurance alone.
• The Part A inpatient coinsurance structure. After the deductible — set at $1,676 per benefit period in 2025 (CMS Medicare Cost Fact Sheet 2025) — daily coinsurance of $419 applies from days 61–90, rising to $838 per "lifetime reserve day" for days 91 and beyond (CMS). Lifetime reserve days are capped at 60 total, ever.
• The skilled nursing facility (SNF) coinsurance gap. Part A covers SNF care fully only for days 1–20. Days 21–100 carry a daily coinsurance of $209.50 in 2025 (CMS). After day 100, Medicare pays nothing.
• The Part B 20% coinsurance without a ceiling. After the annual deductible ($257 in 2025, CMS), beneficiaries owe 20% of all approved outpatient charges with no maximum.

The Part D prescription drug gap has changed substantially since the Inflation Reduction Act of 2022 (Public Law 117-169). The traditional donut hole — a coverage gap between the initial coverage limit and the catastrophic threshold — was effectively eliminated for 2025, with a new $2,000 annual out-of-pocket cap on Part D drug costs (CMS Part D Benefit Parameters 2025).

How it works

The Part A benefit period structure is the mechanism most likely to surprise beneficiaries. A benefit period begins the day a beneficiary is admitted as an inpatient to a hospital or SNF and ends when the beneficiary has been out of inpatient care for 60 consecutive days. There is no limit on the number of benefit periods in a lifetime — meaning the $1,676 deductible can reset and be owed again after each 60-day gap in inpatient care.

The Part B gap operates continuously. Every outpatient service billed under an approved amount triggers a 20% coinsurance liability. For high-cost services — oncology infusions, durable medical equipment, outpatient surgery — a single claim can generate thousands of dollars in cost-sharing. Because Part B has no annual out-of-pocket ceiling, a beneficiary with chronic conditions requiring frequent outpatient treatment faces compounding exposure throughout the calendar year.

For Part D, the 2025 redesign restructured cost-sharing into three phases:

1. Deductible phase — beneficiary pays full drug costs up to $590 (CMS Part D Benefit Parameters 2025).
2. Initial coverage phase — plan and beneficiary share costs until the beneficiary's out-of-pocket spending reaches $2,000.
3. Catastrophic phase — after $2,000 in out-of-pocket costs, the beneficiary pays $0 for the remainder of the calendar year.

Common scenarios

Extended hospital stays. A beneficiary hospitalized for 95 days in a single benefit period would owe the $1,676 deductible, plus 30 days of daily coinsurance at $419 ($12,570), plus 5 lifetime reserve days at $838 ($4,190) — a total exceeding $18,400 before any other charges (CMS).

Post-acute SNF care. Rehabilitation following hip replacement surgery commonly requires 30–45 days in a skilled nursing facility. Days 21–30 carry $209.50 per day in coinsurance, producing more than $2,000 in cost-sharing for a 10-day stretch in the coinsurance window.

Outpatient cancer treatment. Chemotherapy infusions administered in an outpatient hospital setting are billed under Part B. A single infusion session approved at $10,000 generates a $2,000 coinsurance obligation. Repeated cycles across a treatment course can accumulate well above what most beneficiaries budget for.

Excluded services. Routine dental care, routine vision exams, hearing aids, and most long-term custodial care are not covered by Original Medicare at all — a separate category documented in detail at what Medicare does not cover.

Decision boundaries

Two primary structures exist for managing coverage gaps: Medigap (Medicare Supplement Insurance) and Medicare Advantage (Part C).

Medigap vs. Medicare Advantage — core distinction:

Beneficiaries with predictable high utilization — chronic conditions, planned surgeries, ongoing specialist care — generally face lower total annual costs under Medigap Plan G than under Medicare Advantage, because Medigap eliminates the 20% Part B coinsurance with no ceiling. Beneficiaries with low utilization may find Medicare Advantage's lower premiums more cost-effective.

Income-based assistance programs through Medicaid — documented at Medicare low-income assistance programs — can offset gap costs for beneficiaries who qualify. The Medicare Savings Programs pay Part B premiums and, in some cases, cost-sharing directly.

The costs, premiums, deductibles, and copays overview provides the full schedule of standard amounts across all parts, which benchmarks against the gap exposures described here. For beneficiaries beginning to navigate these choices, the Medicare plan finder guide explains how to compare coverage options using the official CMS tool. The full scope of what the program covers and excludes is indexed at nationalmedicareauthority.com.