Short answer
Medicare can add an extra amount, called a late enrollment penalty, to your monthly premium if you sign up late.
Medicare.gov says these penalties are added to your monthly premium.
They are not a one-time late fee.
Part B and Part D have different penalty rules.
This page keeps the Part B rules and the Part D rules separate.
Part B: Medicare.gov says you will pay an extra 10% for each year you could have signed up for Part B, but did not.
Part D: Medicare.gov says you will pay an extra 1% for each month you could have signed up for Part D, but did not, if you go 63 days or more without creditable drug coverage.
This page is general information only. It is not medical advice and it is not benefits advice.
Part B late enrollment penalty
This section is only about Part B.
Medicare.gov says: "You'll pay an extra 10% for each year you could have signed up for Part B, but didn't."
Medicare.gov's example uses full 12-month periods.
Medicare.gov says: "If you waited 2 full years (24 months) to sign up for Part B and didn't qualify for a Special Enrollment Period, you'll have to pay a 20% late enrollment penalty (10% for each full 12-month period that you could have signed up), plus the standard Part B monthly premium."
This page does not print the dollar amounts from that example.
The penalty is added to your monthly Part B premium.
Medicare.gov says it is not a one-time late fee.
Medicare.gov says you will pay the penalty for as long as you have Part B.
Medicare.gov also says you may pay a higher premium depending on your income.
This page does not decide if the Part B penalty applies to you.
Only Medicare can decide that.
When the Part B penalty generally does not apply
Medicare.gov says: "Generally, you won't have to pay a Part B penalty if you qualify for a Special Enrollment Period, or you enroll in a Medicare Savings Program."
On its costs page, Medicare.gov words the Special Enrollment Period rule this way: "To qualify, you (or your spouse) must still be working and you must have health coverage based on that job."
This page does not decide if you qualify for a Special Enrollment Period or a Medicare Savings Program.
Ask Medicare about your own case.
Part D late enrollment penalty
This section is only about Part D, Medicare drug coverage.
Medicare.gov's Part D fact sheet says: "The Part D late enrollment penalty is an extra fee that may be permanently added to your Medicare drug coverage (Part D) monthly premium if you go without Part D or other creditable prescription drug coverage for any period of 63 or more days in a row, after your Initial Enrollment Period is over."
Medicare.gov says you will pay an extra 1% for each month (that's 12% a year) if you:
- Don't join a Medicare drug plan when you first get Medicare, and
- Go 63 days or more without creditable drug coverage.
Medicare.gov's fact sheet gives the formula this way: 1% × national base beneficiary premium × number of full months without Part D or creditable coverage.
Medicare.gov says your penalty depends on how long you went without Part D or other creditable prescription drug coverage.
The monthly penalty is rounded to the nearest 10 cents and added to your monthly Part D premium.
Medicare.gov says it is not a one-time late fee.
Medicare.gov's fact sheet says: "You'll generally pay this penalty for as long as you have Medicare drug coverage, even if you switch plans."
Medicare.gov also says the penalty amount changes each year, and you may pay a higher premium depending on your income.
Medicare.gov says that after you join a Medicare drug plan, the plan will tell you if you have to pay a penalty and what your premium will be.
This page does not decide if the Part D penalty applies to you.
Only Medicare can decide that.
What counts as creditable prescription drug coverage — Part D
This section is only about Part D.
Medicare.gov's fact sheet says: "Creditable prescription drug coverage (also called "creditable coverage") is drug coverage that's expected to pay, on average, at least as much as Medicare drug coverage."
The fact sheet says this could include drug coverage from a current or former employer or union, TRICARE, Indian Health Service (IHS), Tribe or Tribal organization, or Urban Indian program and other health plans.
The fact sheet says: "Your plan must tell you in writing whether your coverage is creditable."
The fact sheet also says: "If you're not sure if your coverage is creditable, contact your plan directly."
Medicare.gov's fact sheet says: "If you don't have Medicare drug coverage, the main way to avoid the Part D late enrollment penalty is to keep creditable prescription drug coverage."
The fact sheet also says to tell your plan about prior creditable coverage.
It says that when you join a plan with Medicare drug coverage, the plan will review Medicare's systems to find out if you had a potential break in creditable coverage for 63 or more days in a row, and if so, the plan will send you a notice, along with a form asking for information about your prior drug coverage.
The fact sheet says it is important to complete, sign, and return the form by the deadline listed on it, and that you can also call your plan to let them know that you had prior creditable coverage.
Medicare.gov's own example — Part D
The dollars in this box, and only in this box, are Medicare.gov's own worked example.
Medicare.gov says the penalty amount comes from the "national base beneficiary premium" ($38.99 in 2026).
Medicare.gov's example says: "If you waited 14 months after you were eligible for Medicare to join a Medicare drug plan, and you didn't have creditable drug coverage, you'll have to pay a 14% late enrollment penalty in addition to your monthly plan premium."
Medicare.gov works the math this way for 2026:
$38.99 (2026 national base beneficiary premium) × 0.14 (14% penalty) = $5.46.
Medicare.gov says $5.46 rounded to the nearest $0.10 = $5.50.
Medicare.gov says: "$5.50 will be your monthly penalty for 2026. This amount is added to your plan's monthly premium for 2026."
Medicare.gov says the national base beneficiary premium changes each year, so your penalty amount may also change each year.
When the Part D penalty generally does not apply
Medicare.gov says generally, you won't have to pay a Part D penalty if:
- You have creditable drug coverage (coverage that's similar in value to Part D), or
- You qualify for Extra Help.
Medicare.gov's fact sheet says: "If you qualify for Extra Help to help you pay Part D premiums, deductibles, coinsurance, and other costs, you won't be charged a late enrollment penalty while you're getting Extra Help."
This page does not decide if you have creditable coverage or if you qualify for Extra Help.
Ask Medicare, or your plan, about your own case.
Ask Medicare about your own case
This page cannot tell you if a penalty applies to you.
It only repeats what Medicare.gov prints.
Medicare.gov's fact sheet says: "Call 1-800-MEDICARE (1-800-633-4227). TTY users can call 1-877-486-2048."
If you are not sure if your drug coverage is creditable, Medicare.gov's fact sheet says to contact your plan directly.
Sources
Every fact on this page comes from Medicare.gov.
- Avoid late enrollment penalties — Medicare.gov — https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
- The Part D Late Enrollment Penalty (fact sheet, CMS Product No. 11222) — Medicare.gov — https://www.medicare.gov/publications/11222-part-d-late-enrollment-penalty.pdf
- What does Medicare cost? — Medicare.gov — https://www.medicare.gov/basics/get-started-with-medicare/medicare-basics/what-does-medicare-cost
This page is general information only. It is not medical advice and it is not benefits advice.