US Medicare Enrollment & Late Penalty Calculator

About the US Medicare Enrollment & Late Penalty Calculator

Work out when you can sign up for Medicare around your 65th birthday, when your coverage starts for each month you could sign up, and what you would pay if you sign up late. Your Initial Enrollment Period is the 7 months around the month you turn 65. If you have health coverage from a job — yours or your spouse’s — while one of you still works, a Special Enrollment Period lets you sign up later without a penalty, for up to 8 months after the job or the coverage ends. Otherwise you wait for the General Enrollment Period, January to March, and pay a late enrollment penalty.

The calculator works out the Part B penalty (10% of the standard premium for each full 12 months you could have had Part B), the Part D penalty (1% of the national base beneficiary premium for each month without creditable drug coverage) and the Part A penalty for people who buy Part A, with the premiums Medicare.gov and CMS publish. Without a pass, the free preview shows the penalties a month in full, with your enrollment periods and the dates coverage starts; a Pro pass unlocks the other amounts, the summary and the CSV. Nothing you enter leaves your browser.

Common uses

• Planning your sign-up before you turn 65, month by month.
• Deciding whether you can keep job-based coverage and delay Part B without a penalty.
• Working out the penalty if you missed your Initial Enrollment Period.
• Checking a Part D penalty after a gap in drug coverage.

Your Initial Enrollment Period

It lasts 7 months: the 3 months before the month you turn 65, that month, and the 3 months after. Sign up in the first 3 months and Part B starts the month you turn 65; sign up in the month you turn 65 or later and it starts the month after (when coverage starts; 42 CFR 407.25). Coverage always starts on the 1st of a month. If your birthday is on the 1st, you reach 65 the day before, so everything moves a month earlier.

Working past 65: the Special Enrollment Period

While you have group health coverage from your own or your spouse’s current work, you can sign up for Part B at any time, and for 8 months after the work or the coverage ends, whichever is first. Sign up while you are still covered, or in the first full month after, and Part B can start that month or up to 3 months later; later in the 8 months it starts the month after you sign up (42 CFR 406.24). COBRA and retiree coverage are not coverage from current work, and COBRA does not change when the 8 months end.

With an employer of fewer than 20 employees, your job-based coverage might not pay without both Part A and Part B, so check with the employer before you delay (when you can sign up).

The Part B late enrollment penalty

The monthly premium goes up 10% for each full 12 months between the end of your Initial Enrollment Period and the month you sign up, leaving out the months you had job-based coverage from current work (42 CFR 408.24). The penalty is added to each year’s standard premium for as long as you have Part B — for most people for life — and the premium with it is rounded to the nearest $0.10. The standard premium is $202.90 a month in 2026 (CMS). Generally there is no penalty if you sign up in a Special Enrollment Period or enroll in a Medicare Savings Program (avoid late enrollment penalties).

The Part D late enrollment penalty

If you go 63 days or more without Part D or other creditable drug coverage after your Initial Enrollment Period, you pay 1% of the national base beneficiary premium for each full month you went without, rounded to the nearest $0.10, for as long as you have Medicare drug coverage (42 CFR 423.46). The base premium is $38.99 in 2026 and $41.33 in 2027 (CMS), so the penalty changes every year. Generally there is no penalty if you qualify for Extra Help.

Part A for people who buy it

Most people get Part A without a premium. If you buy it — $311 a month with 30 to 39 quarters of Medicare-covered work, $565 with fewer than 30, in 2026 — and sign up late, the premium goes up 10%, paid for twice the number of full 12-month periods you could have had Part A but did not sign up (42 CFR 406.33).

Official sources

• Medicare.gov: avoid late enrollment penalties, when coverage starts and when you can sign up
• CMS: Medicare Parts A and B premiums and the Part D base beneficiary premium
• 42 CFR 407.25, 406.24, 408.24, 406.33 and 423.46

Limitations

• For people who get Medicare at 65: people under 65 who get Medicare because of a disability, kidney failure or ALS have other rules.
• Income-related premium increases (IRMAA), other Special Enrollment Periods (for Medicaid, TRICARE, volunteers abroad or exceptional conditions) and Medicare Advantage and Part D plan enrollment periods are not covered.
• The premiums are the 2026 amounts (and the 2027 Part D base premium); the penalties change with each year’s premiums.
• An estimate: Medicare and Social Security decide your enrollment and any penalty; you can ask for a Part D penalty to be reconsidered.

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