Every month a Medicare beneficiary goes without Part D or other creditable prescription drug coverage adds a permanent 1 percent surcharge to the eventual drug premium, according to Centers for Medicare & Medicaid Services guidance updated for 2026. The surcharge is calculated against the national base beneficiary premium, a figure CMS resets annually, and it does not shrink, pause, or disappear once an enrollee later signs up for a plan. That design sets Part D apart from the other two Medicare late-enrollment penalties, both of which work differently, and it means a coverage gap taken in a person’s mid-60s can still be inflating a premium bill two decades later.
The 1 Percent-a-Month Formula Behind the Surcharge
CMS calculates the penalty with a fixed formula published in its Part D late-enrollment-penalty fact sheet: 1 percent of the national base beneficiary premium, multiplied by the number of full months an enrollee went without Part D or other creditable drug coverage after an initial enrollment period closed. The agency’s own worked example shows a beneficiary named Ray, who disenrolled from a Part D plan in August 2024 and did not rejoin coverage until January 2026, accumulating 17 uncovered months. At the 2026 base beneficiary premium of $38.99, a 17 percent penalty adds $6.63 to the monthly bill, rounded under Medicare’s nearest-dime convention to $6.60.
That structure is unusual compared with Medicare’s other two late-enrollment penalties. The Part A penalty, which applies only to beneficiaries who must buy hospital coverage outright, runs for twice the number of years someone delayed enrolling and then stops permanently. The Part B penalty, by contrast, is also lifelong, but it is denominated as a flat 10 percent add-on for each full 12-month period of avoidable delay rather than a monthly compounding rate. Part D’s 1-percent-per-month calculation means even a five- or six-month lapse, which might seem minor next to a multiyear gap, still leaves a measurable and permanent mark on the premium.
The penalty only attaches after a gap of 63 or more consecutive days without creditable drug coverage, meaning coverage CMS expects to pay, on average, at least as much as a standard Medicare drug plan. Employer or union retiree plans, TRICARE, and coverage through the Indian Health Service can all qualify, but the burden falls on the enrollee to document it. When someone joins a Medicare drug plan, the insurer checks CMS’s records for a potential break in creditable coverage and sends a notice with a form requesting proof of any prior coverage the government’s system did not already capture.
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Why a Gap in Coverage Never Stops Costing Money
Once assessed, the surcharge stays attached to the premium for as long as the enrollee keeps Medicare drug coverage of any kind. CMS states that the penalty applies for the duration of an enrollee’s drug coverage, even after switching plans or moving to a plan with no monthly premium. Applied to a longer gap, the arithmetic turns unforgiving: an enrollee who accumulated 24 uncovered months would carry a 24 percent penalty indefinitely, adding $9.36 a month at the 2026 base premium, rounded to $9.40. Held for two decades of retirement, that one gap in coverage would add roughly $2,256 to prescription costs without ever touching what the plan itself charges for drugs.
Because the penalty is set as a percentage rather than a fixed dollar figure, its size still moves every year with the base beneficiary premium the government recalculates annually. A 24 percent penalty locked in during one year is not the same dollar charge the next, since the underlying premium used to calculate it changes as drug plan costs shift nationally. The percentage is frozen at the moment it is assessed, but the base it is multiplied against is not, so the true lifetime cost of a coverage gap is not fixed the day the enrollee finally signs up.
A decision made in a narrow window, generally the seven months surrounding a 65th birthday, can shape a premium bill for the rest of an enrollee’s life. Someone who delays because employer coverage still looks adequate, or who simply assumes Medicare drug coverage can wait, is making a bet with no statute of limitations if the assumption turns out wrong. Unlike a parking ticket or a late credit card payment, there is no point at which the Part D penalty ages off the account.
Extra Help Is the Only Way the Penalty Disappears
The one circumstance in which the penalty stops accruing, or never starts, is enrollment in Extra Help, the federal program that subsidizes Part D premiums, deductibles and coinsurance for beneficiaries with limited income and resources. CMS’s 2026 guidance sets the qualifying income and resource limits at $23,940 and $18,090 for an individual, and $32,460 and $36,100 for a married couple. A beneficiary who qualifies pays no Part D late enrollment penalty for the months covered by Extra Help, regardless of how long a coverage gap ran up to that point.
CMS’s fact sheet illustrates the limits of that protection with a second example, a beneficiary named Kim, who qualified for Extra Help in 2023 and accumulated no penalty for five uncovered months that year. After Kim dropped Part D coverage in mid-2024 and lost Extra Help eligibility in 2025, the twelve months spent without creditable coverage that year did count toward a new penalty, producing a 12 percent surcharge once she rejoined a plan in 2026. The subsidy erases the penalty only for the months it actually covers; a later gap outside the program is treated the same as anyone else’s.
Beneficiaries who dispute a penalty can request a reconsideration through a Medicare contractor independent of their drug plan, which generally rules within 90 days, but they must keep paying the disputed amount while the case is reviewed and even after a loss. No such review, though, can undo a penalty correctly calculated under the formula; the only way this particular cost line ever goes away is if it was wrong from the start, or if income and resources fall low enough to qualify for Extra Help. Absent either outcome, the number set the year coverage lapsed keeps compounding against a beneficiary’s premium for as long as Medicare drug coverage continues.
This article was researched and drafted with the assistance of artificial intelligence.
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