Medicare Late Enrollment Penalty Calculator
How long you went without coverage, and the premiums the penalty is built on
Your result will appear here
Fill in the fields on the left and this updates as you type.
Know what this estimate is based on
- Jurisdiction
- General mathematical model
- Scope and limitations
- Educational estimate only. Confirm the assumptions, current rules, fees, and rounding that apply to your situation before making a decision.
- Source links checked
- Jul 30, 2026
Built and regression-tested by Smart Tools Lab. It has not been individually reviewed by a licensed financial, tax, or legal professional.
How to use
- 01
Enter the months you went without Part B after your Initial Enrollment Period ended, if you had no Special Enrollment Period. The example uses 24 months. If you signed up on time or had employer coverage from a current job, enter 0.
- 02
Enter the full months you went without creditable prescription drug coverage after first becoming eligible. The example uses 14 months. Creditable means the coverage was expected to pay at least as much as standard Medicare drug coverage, and your plan must tell you in writing each year whether yours is.
- 03
Enter how many years you expect to pay the penalty. Both penalties normally last as long as you keep the coverage, so for most people this is the rest of their life; the example uses 20 years.
- 04
Enter your drug plan's own monthly premium so the page can show what the Part D penalty does to it. The standard Part B premium of $202.90 and the national base beneficiary premium of $38.99 are already filled in from CMS.
- 05
Read the monthly penalty for each part, then the yearly and lifetime totals, and compare them with the last figure on the page: what the same delay would have cost with employer coverage, which is nothing.
Formula
Part B penalty = 10% x the number of FULL 12-month periods you could have had Part B and did not, applied to the standard monthly premium. Months that do not complete a twelve-month period are ignored, so 23 months of delay carries the same 10% penalty as 12 months, and the 24th month takes it to 20%. Medicare rounds the resulting total premium to the nearest ten cents. Part D penalty = 1% x the national base beneficiary premium x the number of full, uncovered months without creditable prescription drug coverage, rounded to the nearest ten cents and added to your plan's own premium. The base beneficiary premium is a national figure set by CMS each year, $38.99 for 2026, not your own plan's premium. Monthly penalty = Part B penalty + Part D penalty. Yearly cost = monthly penalty x 12. Lifetime cost = yearly cost x the years you expect to pay it, at today's premiums. Both penalties last as long as you keep the coverage, and both are recalculated each year as the premiums they are based on change.
Example
Someone retires at 65 with no employer coverage, assumes Medicare will find them and does nothing for two years. They go 24 months without Part B and 14 full months without creditable drug coverage before joining a drug plan that charges $40.00 a month. The Part B penalty counts full twelve-month periods: 24 months is exactly two, so the penalty is 20% of the $202.90 standard premium, which is $40.58 a month. Their Part B premium becomes $243.50 once the total is rounded to the nearest ten cents. The Part D penalty counts single months: 14 months is 14% of the $38.99 national base beneficiary premium, which works out at $5.4586 and is rounded to $5.50 a month. Their drug plan premium becomes $45.50. Together the penalties add $46.08 a month, $553 a year. Over the 20 years they expect to pay them, that is $11,059 — and because both are percentages of premiums that rise most years, the real figure will be higher. Had they kept working and stayed on an employer plan from a current job, a Special Enrollment Period would have covered the same delay and both penalties would have been $0.
Definitions
- Initial Enrollment Period
- The seven months around your 65th birthday — the three before, the month itself and the three after — when you can first sign up for Medicare without a penalty.
- Special Enrollment Period
- A window to join Part B without a penalty after the Initial Enrollment Period, given mainly to people covered by a health plan from current employment. For Part B it runs out eight months after that employment or coverage ends.
- Creditable coverage
- Prescription drug coverage expected to pay at least as much as standard Medicare drug coverage. Months with creditable coverage do not count toward the Part D penalty, and the plan must tell you in writing each year whether yours qualifies.
- National base beneficiary premium
- A national Part D figure published by CMS each year and used only to calculate the late enrollment penalty: $38.99 in 2026, up from $36.78 in 2025. It is not what any particular plan charges.
- Late enrollment penalty
- A permanent surcharge added to a Medicare premium for going without coverage when you could have had it. It is paid for as long as you keep the coverage and is recalculated each year.
Good to know
Two penalties, two different clocks
Medicare charges two separate late enrollment penalties, and although people speak of them as one thing, they are calculated in ways different enough to change what a delay costs. The Part B penalty counts completed years. It adds 10% to the standard premium for each full twelve-month period you could have had Part B and did not, and periods that are not complete are ignored entirely. That creates a stepped cost rather than a smooth one: someone who delays 11 months pays no penalty, someone who delays 12 months pays 10%, and someone who delays 23 months still pays only 10%. The example on this page delays 24 months, which is exactly two complete periods, so the penalty is 20% of the $202.90 standard premium — $40.58 a month. Medicare rounds the resulting total to the nearest ten cents, which is why the premium becomes $243.50 rather than $243.48, and the agency's own published example uses these same figures. The Part D penalty counts single months instead, which makes it far more sensitive to a short delay. It adds 1% of the national base beneficiary premium for each full month without creditable prescription drug coverage. That base is a national figure CMS publishes each year, $38.99 for 2026, and it is not the premium any particular plan charges. Fourteen uncovered months therefore means 14% of $38.99, which is $5.4586, rounded to $5.50 and added to whatever the plan itself costs. On a $40.00 plan the premium becomes $45.50. The practical lesson is that the two clocks reward different behaviour. With Part B, if you are already eleven months late, the eleventh and twelfth months are not equivalent — crossing into a completed year costs you 10% for life. With Part D there is no threshold to beat, and every additional month adds its own 1%. Together the two penalties in the example add $46.08 a month, $553 a year, which is the price of two years of inattention.
What creditable coverage means, and why the notices matter
The entire Part D penalty turns on a single phrase, and it is worth understanding precisely. Coverage is creditable when it is expected to pay, on average, at least as much as standard Medicare prescription drug coverage. Months in which you held creditable coverage do not count toward the penalty, so somebody who kept working at 66 with a good employer drug plan and joined Part D at 70 may owe nothing at all, while somebody who went four years with no drug coverage owes 48%. The test is about the quality of the coverage, not whether you had any insurance: a health plan with no drug benefit, or with a thin one, will not protect you. Because this is a judgement about a plan's expected value rather than something an individual can assess, the law puts the duty to say so on the plan itself. Employer, union and retiree drug plans must tell you in writing each year whether their coverage is creditable, usually in a short notice sent before the autumn enrolment window. Those notices are the reason this section exists. They are easy to mistake for junk mail and they are the evidence that settles the question if Medicare later decides you owe a penalty. Keep every one of them, for every year you were covered, and keep them somewhere you will still find them a decade later. If you believe your coverage was creditable and Medicare has concluded otherwise, you can ask for a reconsideration, and those notices are what you will be asked to produce. One further point catches people out. Coverage through an employer only stops the Part D clock for as long as it stays creditable, so if the plan's drug benefit changes, the months that follow can begin to count even though nothing about your own circumstances has changed. That is exactly what the annual notice exists to tell you, and it is why reading the one that arrives each autumn matters even when you have held the same coverage for years. Medicare counts full, uncovered months, and once they have accumulated they are counted for the rest of your life.
The Special Enrollment Period that prevents both
Almost everyone who avoids these penalties does so the same way: by having health coverage from a job that somebody is still doing. If you or your spouse are actively working and covered by that employer's group health plan, you get a Special Enrollment Period allowing you to join Part B later without any penalty, and if the plan's drug coverage is creditable the Part D clock does not run either. In the example on this page, the same 24-month and 14-month delay would have cost nothing instead of $46.08 a month and $11,059 across twenty years. That is the whole of the difference between a costly mistake and an ordinary sequence of events. The traps are all in what counts as current employment, and they are the reason people who thought they were covered discover otherwise. Retiree coverage does not count: the job has ended, so the Special Enrollment Period is not available on the strength of it. COBRA does not count either, for the same reason, and this is perhaps the most expensive misunderstanding in Medicare — someone who leaves a job at 65, elects COBRA for eighteen months and then signs up for Medicare has been accumulating penalty months the entire time. A Marketplace plan does not count. Nor does coverage through a spouse who has themselves retired. The second trap is the deadline. The Part B Special Enrollment Period runs for eight months after the employment or the group coverage ends, whichever comes first, and it does not restart. Someone who takes COBRA at the end of a job and lets eight months pass has lost the protection even though they still hold insurance. There is one further relief worth knowing: Medicare waives the Part B penalty for people enrolled in a Medicare Savings Program, which helps people with limited income and resources. If you are approaching 65 and still working, the safest step is to ask your employer's benefits administrator, in writing, whether the plan counts as current employment coverage and whether its drug benefit is creditable.
Why a fixed number of missed months costs more every year
One feature of both penalties makes them worse over time than the headline figure suggests, and it is easy to miss. Neither penalty is a fixed dollar amount. Each is a percentage, and each is applied to a premium that is recalculated every January. The number of months you missed is settled forever — 24 months of Part B and 14 uncovered Part D months do not change — but the amount those months cost you is recomputed annually against a moving base. For Part D the base is the national base beneficiary premium, which CMS publishes each year. It was $36.78 in 2025 and is $38.99 in 2026, an increase of 6%, which is the maximum the Inflation Reduction Act allows for any year from 2024 through 2029. The 14% penalty in the example therefore cost $5.15 a month in 2025 and $5.50 in 2026, and it will cost more in 2027 without a single additional month of delay. Part B behaves the same way. The standard premium rose from $185.00 in 2025 to $202.90 in 2026, so the same 20% penalty grew from $37.00 to $40.58. This is why the lifetime figure on the page should be read as a floor rather than an estimate. It multiplies today's monthly penalty by the years you expect to pay it, holding premiums still, and produces $11,059 over twenty years in the example. Premiums have not held still in any recent twenty-year period, and if they continue to rise the true cost will be meaningfully higher. There is no mechanism for the penalty to expire, be paid off or be forgiven through good behaviour once it applies. It ends only when the coverage ends, which for Part B and Part D means it ends when you no longer have Medicare. That permanence, more than the size of any single monthly figure, is the argument for treating the enrolment deadlines around your 65th birthday as immovable, and for asking before assuming that the coverage you already hold will protect you.
Frequently asked questions
How much is the Medicare late enrollment penalty?
On this page's example — 24 months without Part B and 14 months without creditable drug coverage — it is $46.08 a month: $40.58 on Part B and $5.50 on Part D. That is $553 a year, and $11,059 over 20 years at today's premiums. The Part B premium rises from $202.90 to $243.50 and a $40.00 drug plan becomes $45.50.
How is the Part B penalty calculated?
It adds 10% to the standard premium for each full 12-month period you could have had Part B and did not. Partial years do not count, so 24 months is exactly two periods and a 20% penalty: 20% of $202.90 is $40.58, making the premium $243.50 once Medicare rounds the total to the nearest ten cents. Medicare's own published example uses these same figures.
How is the Part D penalty calculated?
It counts single months rather than whole years: 1% of the national base beneficiary premium for each full month without creditable drug coverage. In 2026 that base is $38.99, so 14 uncovered months make 14%, which is $5.4586, rounded to the nearest ten cents and added to your premium as $5.50 a month. Because it is a share of a national figure, moving to a cheaper drug plan does not shrink it.
How long do I have to pay it?
For as long as you keep the coverage, which for most people means for life. That is what makes a short delay expensive: 14 uncovered months is a little over a year, but the $5.50 a month that follows never stops. Over the 20 years in the example the two penalties together cost $11,059, and that assumes premiums never rise, which they usually do.
Can I avoid the penalty if I am still working at 65?
Usually, yes. Health coverage from a current job, yours or your spouse's, gives you a Special Enrollment Period to join Part B later without a penalty, and creditable drug coverage stops the Part D clock. The same 24-month and 14-month delay would then cost nothing instead of $46.08 a month. The traps are the kinds of coverage that do not count: retiree coverage, COBRA and Marketplace plans are not current employment, and the Part B Special Enrollment Period runs out eight months after the job or the coverage ends.
Does the penalty change from year to year?
Yes, and it usually grows. Both penalties are percentages of premiums that move: the Part D base beneficiary premium was $36.78 in 2025 and is $38.99 in 2026, with the Inflation Reduction Act capping its annual rise at 6% through 2029, and the standard Part B premium rises most years. The number of months you missed is fixed forever, but the dollar amount attached to it is recalculated every January.
Is the penalty ever waived?
In limited cases. Medicare waives the Part B penalty for people enrolled in a Medicare Savings Program, and a Special Enrollment Period prevents it in the first place. If you believe your coverage was creditable and Medicare has decided otherwise, you can ask for a reconsideration — which is why the annual creditable coverage notices from an employer or union plan are worth keeping. Social Security and CMS decide these cases, not a calculator.