This Medicare late enrollment penalty calculator turns months without coverage into dollars. Enter the months you went without Part B after you could have signed up, the full months you went without a drug plan or creditable drug coverage, and whether you buy hospital insurance. It returns the extra you owe each month, the yearly total, and what the surcharges add up to over time.
The defaults describe a common mistake: 26 counted months late on the medical side, 14 months with no drug benefit, and premium-free hospital coverage. That comes to $40.60 a month plus $5.50, dime rounding included. The last section holds the premium amounts, so you can type in new ones when CMS publishes them.
Medicare Late Enrollment Penalty Calculator
Estimate the Part B, Part D, and purchased Part A late enrollment surcharges from the months you went without coverage, with the dime rounding Social Security and drug plans apply.
Estimates use the 2026 standard Part B premium ($202.90), the 2026 national base beneficiary premium ($38.99), and the 2026 Part A premiums published by CMS, with the counting and rounding rules in SSA POMS and CMS guidance. Your plan and Social Security set the actual amount. Figures change each year; the 2027 Part B premium is expected around November 2026. This is an educational tool, not insurance, tax, or legal advice.
Three Penalties, Three Different Rules
Medicare late enrollment penalties follow a separate rule for each type of coverage.
| Coverage | Rate | Applied to | How long |
|---|---|---|---|
| Hospital (A), if bought | 10%, flat | $311 or $565 premium | Twice the full years you waited |
| Medical (B) | 10% per full 12 months | Standard premium, $202.90 | For life, with one exception |
| Drugs (D) | 1% per full uncovered month | National base beneficiary premium, $38.99 | As long as you have Medicare drug coverage |
About 99% of beneficiaries get premium-free Part A, per CMS, because they or a spouse paid payroll taxes for at least 40 quarters. So the first row rarely applies. The other two are the ones people trigger by accident: someone retires at 64, keeps a retiree plan or COBRA, and assumes that counts. It doesn’t.
Medicare Part B Penalty: 10% for Each Full Year You Waited
The Part B late enrollment penalty is 10% of the standard monthly premium for each full 12-month period you could have had it and didn’t. Your initial enrollment period is the window around the month you turn 65. Once your initial enrollment period ends, Social Security counts each month through the month you sign up, drops months when you were 65 or older on a group plan through your own or a spouse’s current job, divides by 12, and ignores the remainder.
So 23 counted months is one period (10%), and 26 months is two (20%).
The penalty is calculated on each year’s standard Part B premium, so the dollar amount climbs whenever the base does. Medicare.gov’s example uses 24 months: $202.90 plus 20% ($40.58) is $243.48. SSA’s program manual rounds premiums to the nearest dime, 5 cents and up going higher, so the bill reads $243.50. The true cost is $40.60, not $40.58.
| Full periods late | Monthly bill | Extra each month |
|---|---|---|
| 1 (10%) | $223.20 | $20.30 |
| 2 (20%) | $243.50 | $40.60 |
| 5 (50%) | $304.40 | $101.50 |
| 10 (100%) | $405.80 | $202.90 |
Income is a separate charge: higher earners also owe IRMAA on the monthly premium for Part B, which our IRMAA calculator estimates. The one exception to “for life”: people who join Medicare before 65 on disability have any surcharge rolled back to the standard rate the month they turn 65 (POMS HI 01001.010).
The Part D Penalty Calculator Formula, Rounding Included
The Medicare Part D late enrollment penalty is 1% of the base beneficiary premium times the full months you went without Part D or creditable coverage after your enrollment window closed. A gap only counts once it runs 63 days or more in a row.
CMS sets the base every summer, and the national base beneficiary premium changes every year, so the same percentage costs a different amount each January. It’s $38.99 now. The next figure is out: $41.33, exactly 6% higher, the most the Inflation Reduction Act allows in a year through 2029.
Fourteen uncovered months: 0.14 times $38.99 is $5.4586, rounded to the nearest $0.10, so the monthly penalty for 2026 is $5.50. In 2027 the same 14% becomes $5.80.
| Uncovered months | At $38.99 | At $41.33 (2027) |
|---|---|---|
| 6 | $2.30 | $2.50 |
| 12 | $4.70 | $5.00 |
| 24 | $9.40 | $9.90 |
| 60 | $23.40 | $24.80 |
It’s an amount that is permanently added to your Medicare Part D premium each month. The penalty is added to your plan premium by your Part D plan, even a $0 one, and it follows you when you switch. You carry it as long as you have Medicare.
Creditable prescription drug coverage is prescription drug coverage that’s expected to pay, on average, at least as much as the standard benefit. TRICARE, the Indian Health Service, and many employer and union plans qualify, and the plan must tell you in writing. Keep those letters as proof.
Part A Late Enrollment Penalty When You Have to Buy Hospital Coverage
With 40 quarters of work (yours or a spouse’s), skip this. With fewer, you buy it: $311 a month with 30 to 39 quarters, $565 with fewer than 30. Wait 12 months or more and that premium goes up 10%.
This one is flat and temporary. You pay the higher premium for twice the number of full 12-month periods you could have enrolled and didn’t. At 26 months late with 35 quarters, 10% of $311 is $31.10 a month for four years, $1,492.80 in all.
One Retiree, Three Numbers: Walking Through the Defaults
Picture a retiree whose first sign-up window closed while she had a health plan from her old employer. Retiree coverage isn’t coverage from current work, so Social Security counted 26 months before she signed up. Her retiree drug benefit fell short of Medicare’s standard, and it took her 14 months to join a Medicare drug plan.
- Medical: two full periods, 20%, a $243.50 bill, $40.60 over standard.
- Drugs: 14% of $38.99, rounded to $5.50.
- Hospital: premium-free, so nothing.
Together that’s $46.10 a month and $553.20 a year. Over 20 years at current premiums it’s $11,064, and since both bases have tended to rise, the real total will likely be higher. She’ll pay a late enrollment penalty for as long as she keeps coverage, all for two years she chose to go without it.
We tested this tool against the published CMS examples (24 months of medical coverage at $243.50; 14, 12, and 17 uncovered drug months at $5.50, $4.70, and $6.60), and it matches each one to the cent.
Coverage That Stops the Clock, and Coverage That Doesn’t
If you or your spouse still works and you’re on that employer’s group plan, delayed enrollment is safe. When the job or the coverage ends, whichever is first, you have eight months to sign up for Part B without a penalty, whether or not you take COBRA.
- Group coverage from a current job, yours or a spouse’s: stops the medical count and lets you qualify for a special enrollment period.
- COBRA and retiree plans: don’t stop it. The eight months start when the job ends.
- Employer, union, or TRICARE drug benefits that pass the test: stop the drug count only.
- A Medicare Advantage plan with drugs counts as Part D enrollment.
- A Medicare Savings Program: enrolling generally cancels the medical charge.
The simple rule: when you’re eligible for Medicare, either sign up for Medicare or confirm in writing that your coverage comes from active work. Most penalties start with someone assuming a Medicare plan would wait. Miss the Special Enrollment Period and you’re left with January 1 to March 31, with every month since you were first eligible to sign up counted.
Can Medicare Late Enrollment Penalties Be Removed or Reduced?
Usually not. Part B and Part D penalties are permanent unless the count is wrong. Where you have room:
- Reconsideration. Return the form in your plan’s notice within 60 days of the letter. An independent contractor decides, generally within 90 days, and you keep paying meanwhile.
- Extra Help. You avoid the Part D penalty if you qualify, and months before you qualified aren’t counted.
- Miscounted months. Group coverage through current work is excluded by rule; if Social Security counted it, send proof.
Switching to Medicare Advantage won’t help: you still pay a penalty on the medical side. Start by pulling your enrollment dates and coverage letters, count the full months, and run the numbers before you sign up, since one more month can cross into a new 12-month period.
Frequently Asked Questions
How much is it?
Part B adds 10% of the standard premium per full year late. Part D adds 1% of the base premium per full uncovered month. Bought Part A adds a flat 10% for twice the years you waited.
Is there a penalty for not signing up at 65?
The penalty applies only if you don’t enroll and lacked a group plan from current work (medical) or creditable drug benefits.
Does waiting longer cost more?
Yes. The Part B penalty adds 10% for each additional full year, and you’d pay a Part B surcharge on each new year’s premium.
What is the base premium for 2026?
$38.99, rising to $41.33 for 2027.
When will I know my exact penalty amount?
Your drug plan tells you after you join, and Social Security lists the medical figure on your premium notice. A Medicare penalty calculation here should match both.
Does the drug charge count each month you were without coverage?
Each full month after your window, across gaps of 63 days or longer.
Figures last reviewed September 2026: premiums from the CMS premium fact sheet and CMS Part D bid releases; rules from CMS and SSA POMS. The next standard medical premium is expected around November. Estimates only; this page is educational and is not insurance, tax, or legal advice.