Medicare attaches penalties to late enrolment in Part B and in Part D, and the important thing about both is the word permanent: they are not a one-off charge but an addition to the premium for as long as the coverage is held. Each is worked out from a published rule and a count of months, which is why the sum turns out to be simpler than the question suggests.
The Part B penalty
The Part B penalty is a percentage added to the premium for each full year a person could have had Part B and did not, when they were not covered by a qualifying arrangement such as employment coverage. It is then payable for as long as they have Part B. Because the surcharge is a percentage of a premium that itself rises, the amount grows over time even though the percentage does not. The base it is applied to in 2026 is $202.90 each month.
The Part D penalty
The Part D penalty reads months rather than years. It is calculated from the number of full months a person went without creditable drug coverage after becoming eligible, applied against a national base figure that Medicare publishes annually, and added to the drug plan premium for as long as drug coverage is held. Creditable is the operative word: coverage from an employer or a union may count, and whether it does is something the provider of that coverage states.
Why no calculator is really needed
Both sums are a published rate multiplied by a count of periods, and the count is the only input a person has to establish. A calculator adds nothing except the risk of using an out-of-date base figure. What is worth doing instead is establishing whether the coverage held during the gap was creditable, because that decides whether any penalty applies at all, and the free counselling service in every state will read the paperwork with you.
Questions people ask about late enrollment penalty
Does the penalty ever stop?
Generally no. Both penalties are added to the premium for as long as the coverage is held.
What counts as creditable drug coverage?
Coverage at least as good as Part D. The organisation providing it is required to tell you whether it is, and that notice is worth keeping.
Does employer coverage protect me from the Part B penalty?
Qualifying current employment coverage can. The rules turn on the kind of coverage and the size of the employer, and Medicare's pages set them out.
Can a penalty be appealed?
There is a reconsideration process for the Part D penalty. Your State Health Insurance Assistance Program will explain how it works, free.