Three penalties exist, they are calculated three different ways, and the phrase that protects you from two of them is “creditable coverage”. This guide sets out each calculation with Medicare’s own worked examples, because the amounts are smaller than people fear and the duration is longer than they expect.
Part B: 10 percent a year, for life
You pay an extra 10 percent for each full 12-month period you could have signed up for Part B but did not. The penalty is added to the standard premium and you pay it for as long as you have Part B.
Medicare’s worked example: someone who waited two full years and did not qualify for a Special Enrollment Period pays a 20 percent penalty. In 2026 that is $202.90 plus $40.58, which is $243.48, rounded to $243.50 a month.
Because the penalty is a percentage of the standard premium and the standard premium rises most years, the penalty amount rises with it. It is not frozen at the figure you first saw.
Part D: 1 percent a month, for life
The Part D penalty is 1 percent for each month — 12 percent a year — that you went without creditable drug coverage after first becoming eligible, or any period of 63 days or more without it.
It is calculated from the national base beneficiary premium, not from your own plan premium. Medicare’s example: 14 months without creditable coverage gives a 14 percent penalty; against the 2026 base of $38.99 that is $5.46, rounded to $5.50 a month, added to whatever your plan charges.
The penalty follows you if you switch plans, and the base premium changes each year, so the amount moves.
Part A: the one that ends
Most people never meet this one, because most people get Part A premium-free. If you have to buy Part A and do not do so when first eligible, the monthly premium may go up 10 percent.
Unlike the other two, it is not permanent: you pay the higher premium for twice the number of years you did not sign up. Two years late means four years of the higher premium, and then it stops.
What prevents a penalty
| Part A | Part B | Part D | |
|---|---|---|---|
| Rate | 10% of the premium | 10% per full 12 months missed | 1% per month missed |
| Calculated from | Your Part A premium | The standard Part B premium | The national base beneficiary premium |
| How long | Twice the years you delayed | As long as you have Part B | As long as you have drug coverage |
| Main way out | A Special Enrollment Period | A Special Enrollment Period, or a Medicare Savings Program | Creditable drug coverage, or Extra Help |
Source: Medicare.gov, Avoid late enrollment penalties. Figures used in the examples are 2026 amounts.
Two things are worth drawing out. Enrolling in a Medicare Savings Program means you generally will not pay a Part B penalty, and getting Extra Help means you will not pay a Part D one — so the programmes in the Extra Help guide are penalty protection as well as cost help.
And “creditable coverage” is a defined test, not a judgement call. Employer drug coverage is usually creditable and the plan has to tell you in writing each year whether it is. Keep those letters; they are the evidence if a penalty is ever assessed against you in error.
Frequently asked questions
Is a late enrollment penalty a one-time fee?
No. It is added to your monthly premium. For Part B and Part D that is for as long as you hold the coverage, which for most people means for life.
How much is the Part B penalty exactly?
Ten percent of the standard premium for each full 12-month period you could have enrolled and did not. Medicare’s 2026 example: two years late is a 20 percent penalty, making the monthly premium $243.50 rather than $202.90.
I had drug coverage through my employer. Do I owe a Part D penalty?
Generally not, provided the coverage was creditable — similar in value to Part D. Your plan must tell you in writing each year whether it is, and that notice is what you produce if a penalty is assessed in error.
Does the Part A penalty last forever?
No, and it is the only one that does not. You pay the higher Part A premium for twice the number of years you delayed, and then it stops.
Sources
- Avoid late enrollment penalties — Medicare.gov · read 2026-10-19
- 2026 Medicare Parts A & B Premiums and Deductibles — Centers for Medicare & Medicaid Services · 2025-11-14 · read 2026-10-19
- Medicare drug coverage (Part D) costs — Medicare.gov · read 2026-10-19
This guide explains published rules and figures, with the source for each one. It is not advice about your own situation.