Medicare Late Enrollment Penalty Calculator (Part B and Part D, 2026–2027)

Work out your Medicare Part B and Part D late enrollment penalties: the months that count, the percentage, the monthly dollars, how an employer plan and Extra Help change it, and the sign-up month where each 10% step starts. From the CMS rules and examples.

Medicare charges two different late penalties and counts them differently. Part B (medical) adds 10% of the standard premium for every full 12 months you could have had it and did not, for as long as you have Part B. Part D (drug coverage) adds 1% of a national base premium for every full month you went without Part D or other creditable drug coverage, once the gap reaches 63 days. Enter your dates to see the months that count and the dollars; the examples in the questions below are the ones Medicare itself prints.

Month and year you were or will be born (turn 65 in year + 65)

My birthday is on the 1st of the month (Medicare counts you as 65 the day before, so everything starts a month earlier)

Your Initial Enrollment Period is the 7 months from March 2024 through September 2024.

Part B (medical insurance)

Month you sign up (or will sign up) for Part B

I was covered by an employer health plan through my own or my spouse's current work, from the month I turned 65Years you expect to pay Part B (for the lifetime total)

Part D (drug coverage)

My Medicare Part A or Part B started after the month I turned 65

First month your Part D plan covers you

I had other drug coverage that counts as creditable (employer, union, TRICARE, VA) after my Part D enrollment period endedI dropped Part D (or other creditable coverage) later and joined again — a second gapI get Extra Help (the low-income subsidy) with my Part D premiumsPart D premium year

Part B late enrollment penalty

20%+$40.60 a month, for as long as you have Part B

28 months count (from October 2024 through January 2027), which is 2 full 12-month periods. Part B would cost $243.50 a month at the 2026 standard premium of $202.90. That is $487.20 a year and about $9,744.00 over 20 years if the premium stayed at its 2026 level (it changes every year).

Only complete 12-month periods count: the next 10% step comes 8 months later in the count. Higher-income premiums (IRMAA) are on top of this.

First sign-up month that carries each Part B penalty step
Sign up in	Penalty	Part B a month (2026)
September 2025 or later	10%	$223.20
September 2026 or later	20%	$243.50
September 2027 or later	30%	$263.80

Outside a Special Enrollment Period you can sign up only from January 1 to March 31; coverage starts the month after you sign up.

Base: the 2026 standard Part B premium of $202.90. CMS has not published the 2027 amount yet (expected in the autumn).

Part D late enrollment penalty (2027)

+$11.20a month, added to your plan's premium

27 uncovered months × 1% × the 2027 base premium of $41.33 = 27%, which is $11.16 before CMS rounds it to the nearest 10 cents. That is $134.40 a year, and the penalty is recalculated every year as the base premium changes.

Gap after your Initial Enrollment Period: 27 months from October 2024
Your Part D Initial Enrollment Period ended after September 2024 (three months after your first month of Part A or Part B, June 2024).

Not modelled: Medicare that starts before 65 because of disability or kidney failure, or Part A through a later application; the exceptional-conditions Special Enrollment Periods (emergencies, a misleading employer or plan, release from prison, loss of Medicaid); a Medicare Savings Program or state help paying Part B; the Part A penalty; Part B income-related surcharges; and the way a plan counts days rather than months (a Part D gap is charged only if it lasts 63 days or more in a row, which is 3 whole months here). Employer coverage counts only if it is through current work: retiree coverage and COBRA do not. Check the dates with Social Security (Part B) or your drug plan (Part D), which make the actual decision.

Estimate only, from the Medicare regulations and the Centers for Medicare & Medicaid Services' published examples. Not financial, tax or legal advice, and not an enrollment decision: if you think you were charged a penalty in error, a Part D plan will send a reconsideration form with the notice, and Social Security handles Part B questions.

Frequently asked questions

Q.How is the Part B penalty worked out?

The standard premium goes up 10% for each full 12 months in the period between the end of your Initial Enrollment Period and the close of the month you first enrolled, leaving out months you were covered by an employer plan through current work (42 CFR 408.22 and 408.24). Medicare.gov's example: wait 24 full months and you pay a 20% penalty, $202.90 + $40.58 = $243.48, rounded to the nearest 10 cents, $243.50 a month in 2026. The calculator reproduces it: an Initial Enrollment Period that ended in March 2024 and a sign-up in March 2026 leave 24 months, 20%, $243.50 a month.

Only complete 12-month periods count. With the same March 2024 end, a sign-up in February 2025 counts 11 months and carries no penalty; March 2025 counts 12 and carries 10% ($20.30 a month more than the standard premium). The penalty lasts as long as you have Part B, and because it is a percentage of the standard premium, it grows when the premium does.

Q.Does employer coverage let me skip Part B without a penalty?

Often, but only if the coverage is a group health plan through your own or your spouse's current work. Social Security says COBRA and retiree health plans are not coverage based on current employment, so you get no Special Enrollment Period when they end, and that a plan (or the job it rests on) that ends while your Initial Enrollment Period is still open gives none either. If you do qualify, you can sign up for Part B while you are covered or in the eight months after the coverage or the work ends, whichever comes first, with no penalty (42 CFR 406.24; 407.20). The calculator's example: coverage through December 2026 and a sign-up in August 2027 is inside the window (no penalty); wait until January 2028 and the 13 months since the coverage ended count, 10%. CMS describes the same counting: for enrollments after the Initial Enrollment Period, months with group health plan coverage are left out. Ask your plan whether it is group health plan coverage; Medicare.gov says retiree coverage may not be.

Q.How is the Part D penalty worked out, and when does a gap count?

It is 1% of the national base beneficiary premium for each full month you could have had Part D and did not, rounded to the nearest 10 cents and added to your plan's premium (42 CFR 423.286(d)(3); CMS fact sheet). The base premium is $38.99 in 2026 and $41.33 in 2027 (CMS, July 28, 2026). CMS's example: Ray had no coverage for 17 months, so 17% × $38.99 = $6.63, charged as $6.60 a month. The calculator gets 17 months and $6.60for 2026 and $7.00 for the same 17 months in 2027.

A gap counts only once it reaches 63 days in a row after your Part D Initial Enrollment Period (42 CFR 423.46); CMS's example of 61 days (May 1 to June 30) is not charged. In whole months that is three: one or two missing months charge nothing, three or more charge every month from the first. Separate gaps add up, and there is no cap.

Q.Does the Part D penalty ever go away?

It is charged for as long as you have Part D, even if you change plans or join one with a $0 premium. It is not billed while you get Extra Help, and months before you qualified for Extra Help are not counted. If you had Medicare because of a disability and later turn 65, the new Initial Enrollment Period around your 65th birthday ends the old penalty. If you drop Part D, the penalty stops; if you rejoin you owe the earlier penalty plus any new gap (CMS Part D guidance, chapter 4, section 20.6). You can ask for a reconsideration within 60 days of the date on the notice, with proof of creditable coverage such as an employer notice; you must keep paying while it is decided.

Q.Why does the calculator use 2026 for Part B?

CMS has not announced the 2027 standard Part B premium as of October 22, 2026 (the Trustees project it higher). Part D uses 2026 or 2027 because CMS published the 2027 base beneficiary premium on July 28, 2026. When CMS announces the 2027 Part B premium this calculator will be updated; until then Part B dollars are at the 2026 premium of $202.90.