If you sign up for Part B late and didn't qualify for a Special Enrollment Period, or go without Part D or other creditable drug coverage, you could owe a penalty. It's added to your monthly premium. It's not a one-time fee, and you usually keep it for as long as you have that coverage.
The amounts
2026
2027
National base beneficiary premium (used to figure the Part D penalty)
$38.99Official
$41.33Official
What matters most
Part B: 10% for each year late
For Part B (medical insurance), the penalty adds 10% to your premium for each full 12-month period you could have signed up but didn't.
Part D: 1% for each month late
For Part D (drug coverage), the penalty is 1% of a national base amount for each full month you could have had Medicare drug coverage but didn't, and didn't have other creditable drug coverage. For 2027 that base amount is $41.33. The penalty is added to your monthly premium.
There are ways to avoid it
You generally won't owe this penalty if you have creditable drug coverage, meaning coverage that's similar in value to Part D. And if you or your spouse are still working, you may be able to wait to sign up without a penalty.
Want the detail? How it works, a worked example and common mix-ups are in .
Words on this page
Late enrollment penalty
an extra amount added to your monthly premium for signing up after you were first eligible, usually for as long as you have the coverage
Creditable coverage
other drug coverage that's at least as good as Medicare's, so it protects you from the Part D late penalty
National base beneficiary premium
a set dollar amount Medicare uses to figure the Part D penalty, which is $41.33 in 2027
Who can answer for your situation
1-800-MEDICARE can explain a penalty on your bill, Social Security handles Part B sign-up and penalty questions, and your State Health Insurance Assistance Program (SHIP) offers free help.
If money is tight, Extra Help can lower what you pay for Medicare drug coverage.
How the Part B penalty adds up
The penalty is 10% for each full 12-month period you could have signed up for Part B but didn't. So a 2-year gap works out to a 20% higher premium.
In 2026, the standard Part B premium is $202.90 a month. With a 20% penalty, that example works out to $243.50 a month.
How the Part D penalty works
For drug coverage, Medicare multiplies 1% times a national base amount, times the number of full months you could have had Medicare drug coverage but didn't, and didn't have other creditable drug coverage. The result is rounded and added to your monthly premium. That base amount is $41.33 in 2027 ($38.99 in 2026).
This penalty usually lasts for as long as you have Medicare drug coverage, even if you switch plans.
An example
Say you were eligible for 14 months and didn't have creditable drug coverage. You'd owe a 14% penalty, added to your drug plan's monthly premium.
When it counts as a gap, and how to catch up
For drug coverage, the penalty applies if you go 63 or more days in a row when you don't have Medicare drug coverage or other creditable coverage.
If you missed your first window to sign up for Part B, your Initial Enrollment Period, you can sign up during the General Enrollment Period, January 1 to March 31. Your coverage starts the month after you sign up, and you might pay a penalty if you don't qualify for a Special Enrollment Period.
Common mix-ups
These are the pairs people most often mix up.
Not a one-time fee
A late penalty isn't a single charge. It's added to your monthly premium and usually stays for as long as you have that coverage.
Part A penalty is different
The Part A penalty is different. It applies only if you have to buy Part A, because you don't qualify for premium-free Part A, and you don't buy it when you're first eligible. Your premium may go up 10%, and you pay the penalty for twice the number of years you didn't sign up.
1 What the source says · Part B late enrollment penalty
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 ($202.90 in 2026).
Checked September 27, 2026
3 What the source says · Part D late enrollment penalty
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
Checked September 27, 2026
10 What the source says · Late enrollment penalties
Late enrollment penalties: Are added to your monthly premium. Are not a one-time late fee. Are usually charged for as long as you have that type of coverage (for most people, that's a lifetime penalty).
Checked September 27, 2026
11 What the source says · Part A late enrollment penalty
The Part A penalty is different.
Checked September 27, 2026
12 What the source says · Part A late enrollment penalty
If you have to buy Part A, and you don't buy it when you're first eligible for Medicare, your monthly premium may go up 10%. You'll have to pay the penalty for twice the number of years you didn't sign up
Checked September 27, 2026
13 What the source says · Part A late enrollment penalty
Some people have to buy Part A because they don't qualify for premium-free Part A.
2 What the source says · How much is the Part D late enrollment penalty?
The Part D late enrollment penalty is calculated by multiplying 1% times the “national base beneficiary premium” ($38.99 in 2026) times the number of full, uncovered months you were eligible to join Medicare drug coverage but didn't (and didn't have other creditable prescription drug coverage). That amount is rounded to the nearest $.10 and added to your monthly premium.
Checked September 27, 2026
4 What the source says · Part D late enrollment penalty
The Part D late enrollment penalty is added to your premium for as long as you have Medicare drug coverage, even if you switch plans.
Checked September 27, 2026
5 What the source says · When you may owe a late enrollment penalty
You may owe a late enrollment penalty if at any time after your Initial Enrollment Period is over, there's a period of 63 or more days in a row when you don't have Medicare drug coverage or other creditable prescription drug coverage
Checked September 27, 2026
6 What the source says · Part D late enrollment penalty example
If you waited 14 months 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.
Checked September 27, 2026
CMS.gov
Medicare Part D 2027 National Average Monthly Bid Amount Information
9 What the source says · After your Initial Enrollment Period ends, and the General Enrollment Period
After your Initial Enrollment Period ends, you can only sign up for Part B and premium-Part A during one of the other enrollment periods. Between January 1-March 31 each year (General Enrollment Period) You can sign up between January 1-March 31 each year. This is called the General Enrollment Period. Your coverage starts the month after you sign up. You might pay a monthly late enrollment penalty, if you don't qualify for a Special Enrollment Period.
Checked September 27, 2026
Something look wrong?
If something here doesn’t match what you’ve been told, please check with 1-800-MEDICARE, and let us know through our Contact page.
General education, not individualized advice. For your own situation, you can call 1-800-MEDICARE or your State Health Insurance Assistance Program (SHIP).
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