Part B late-enrollment penalty estimate

Enter your birth date, the month you will sign up (or did), and any months after your sign-up window when a job-based plan covered you. The estimate follows the federal counting rule and uses the current standard premium.

How the estimate is worked out

For people who first sign up on or after January 1, 2023, the penalty counts the months between the end of your Initial Enrollment Period and the end of the month you sign up. Months when you were covered by a group health plan through your own or your spouse's current job are left out.¹

Each full 12 months adds 10% to your Part B premium. Partial years don't count.² So 23 months adds 10%, and 24 months adds 20%.

For a sign-up before 2023, the count ran to the end of the enrollment period you signed up in, not the month you signed up. The estimate handles the General Enrollment Period case, where the count ran through March 31 and Part B started on July 1.³ A sign-up before 2023 in any other month after your window was in a Special Enrollment Period, which needs dates the estimate doesn't ask for, so it says so instead of guessing.

The dollar figure applies the percentage to the standard premium, $202.90 a month⁴ for 2026, and rounds the total to the nearest 10 cents, the way Medicare.gov's own example does.² The 2027 standard premium had not been announced when this page was last checked.⁵ Because the penalty is a percentage, its dollar amount changes whenever the standard premium does.

What the estimate can't know

Whether you qualify for a Special Enrollment Period. If job-based coverage from current work covered you, enter those months. COBRA and retiree coverage don't count.⁶
Exceptional situations. Disasters, wrong information from an employer or plan, and some other situations can give you a Special Enrollment Period, and months covered by one are left out of the count.⁷
Help with costs. Medicare.gov says you generally won't pay a Part B penalty if you enroll in a Medicare Savings Program.⁸
Income. People with higher incomes pay a larger Part B premium, which this estimate leaves out. In 2026 that starts above $109,000 for a single return, $218,000 for a joint return⁹, judged from your tax return for 2024.¹⁰

Social Security and Medicare make the actual decision. Treat this as a way to see the size of the problem before you call them, not as their answer.

When sign-ups are taken

Outside your Initial Enrollment Period, and without a Special Enrollment Period, you can sign up only from January 1 to March 31. Coverage then starts the month after you sign up.¹¹ If you pick a sign-up month outside January to March, the estimate tells you so.

A worked example

Someone who turned 65 in June 2024, with no job coverage, had a window ending September 30, 2024. Signing up in March 2027 counts 30 months: two full 12-month periods, so 20%. Their Part B would start April 1, 2027. The full explanation, with Medicare.gov's own example, is in the Part B penalty and how to avoid it.

Private by design

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Other tools

Your Medicare sign-up window at 65Enter your birth date to see the seven months when you can first sign up for Medicare Parts A and B, and the date Part B would start for each month.
Full retirement age: your month, and what starting early or late doesEnter your birth date to find your Social Security full retirement age, the month you reach it, the earliest month you can start, and the percentage of your full benefit at every age from 62 to 70.
RMD age by birth year: when required minimum distributions startEnter your birth date to find the age your required minimum distributions start, the year of your first RMD, and its deadline. With the full table by birth date.
All your dates on one pageThe planner: every date from 50 to 75, worked out from your birthday, ready to print.

Sources for this page

Which months count toward the Part B penalty (sign-ups from January 1, 2023: to the end of the month you sign up). Source: Electronic Code of Federal Regulations, 42 CFR 408.24: Which months count toward the penalty. Checked October 25, 2026.
Part B late-enrollment penalty: 10% for each full 12 months, usually for as long as you have Part B. Source: Medicare.gov, Avoid late enrollment penalties; Electronic Code of Federal Regulations, 42 CFR 408.22: Increased premiums for late enrollment. Checked October 25, 2026.
Sign-ups before 2023: the penalty count ran to the end of the enrollment period you signed up in (March 31 for the General Enrollment Period), and General Enrollment Period coverage started July 1. Source: Electronic Code of Federal Regulations, 42 CFR 408.24: Which months count toward the penalty; Electronic Code of Federal Regulations, 42 CFR 407.25: Beginning of entitlement. Checked October 25, 2026.
Part B standard monthly premium. $202.90 a month (2026). Source: Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet), November 14, 2025. Checked October 25, 2026.
Part B standard monthly premium. not yet announced. Source: Centers for Medicare & Medicaid Services, CMS Newsroom. Checked October 25, 2026.
COBRA and retiree coverage don't count as job-based coverage for the Special Enrollment Period. Source: Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.
Special Enrollment Periods for exceptional situations, from January 1, 2023. Source: Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.
Medicare Savings Programs help people with limited income pay Medicare costs; enrolling generally means no Part B penalty. Source: Medicare.gov, Avoid late enrollment penalties; Centers for Medicare & Medicaid Services, Medicare Advantage and Medicare Prescription Drug Programs Expected to Remain Stable in 2027 (press release), September 28, 2026. Checked October 25, 2026.
Income above which Part B costs more (2026). $109,000 for a single return, $218,000 for a joint return (2026). Source: Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet), November 14, 2025. Checked October 25, 2026.
The higher Part B premium is based on income on your tax return from two years before (2024 for 2026). Source: Medicare.gov, Medicare costs. Checked October 25, 2026.
General Enrollment Period: January 1 to March 31; coverage starts the month after you sign up. Source: Electronic Code of Federal Regulations, 42 CFR 407.15: General enrollment period; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Every figure on the site, with its source and checked date, is on the sources page.