Medicare Part B Late Enrollment Penalty Calculator (2026): The 10% Rule Explained

If you missed your Initial Enrollment Period, or you are leaving a job or COBRA after 65, you may be wondering whether you owe a penalty. This guide works as a Medicare Part B late enrollment penalty calculator: it explains the 10% rule, walks through Medicare.gov's own 2026 example, and covers the traps that create the penalty.

Quick answer: how the Part B late penalty works

The penalty adds 10% of the standard Part B premium for each full 12-month period when you could have had Part B but did not sign up. The 2026 standard Part B premium is $202.90 a month.

The penalty is not a one-time fee. It is added to your monthly premium every month. In most cases you pay it for as long as you have Part B, which for most people means for life.

Because the penalty is a percentage of the standard premium, the dollar amount rises each year when the standard premium rises.

Only full 12-month periods count

Months without Part B (when you could have had it)	Penalty
11 months or fewer	Nothing added
12 to 23 months	10%
24 to 35 months	20%

The pattern continues in the same way for longer gaps. For example, 36 months gives a 30% penalty.

The 2026 math: Medicare.gov's worked example

Medicare.gov's official 2026 example is someone who waited 24 months and did not qualify for a Special Enrollment Period. That person has a 20% penalty. Here is the math step by step:

1. Start with the 2026 standard premium: $202.90.
2. Add the 20% penalty: $40.58.
3. Total: $202.90 + $40.58 = $243.48.
4. Social Security rounds Part B premium amounts to the nearest 10 cents (5 to 9 cents round up), so the monthly premium is $243.50.

Two more examples use the same 10% rule. Twelve months without Part B gives $223.19, rounded to $223.20 a month. Thirty-six months gives 30%, or $263.77, rounded to $263.80 a month. A 20% penalty adds about $486.96 over 12 months in 2026.

The penalty is figured on the standard premium. People with higher incomes may also pay an income-related monthly adjustment amount (IRMAA) on top of the premium. The Part B annual deductible for 2026 is $283.

Which months count

Months inside your Initial Enrollment Period are never counted. That period lasts 7 months. It starts 3 months before the month you turn 65 and ends 3 months after the month you turn 65.

For people signing up for the first time on or after January 1, 2023, Social Security counts the months after the Initial Enrollment Period ends through the end of the month you enroll.

Months when you had group health plan coverage based on current employment are handled through the Special Enrollment Period, covered below.

Try the calculator

Enter the number of full months you went without Part B after your Initial Enrollment Period, and the calculator will work out your estimate.

Part B late penalty estimator (2026)

Months you went without Part B after your Initial Enrollment Period ended

Do not count months when you (or your spouse) had group health coverage from a current job. Do count months on COBRA or retiree coverage.

Estimate only, using the 2026 standard Part B premium of $202.90. Income-related amounts (IRMAA) are not included. Social Security decides your actual penalty.

Your actual penalty is decided by Social Security, so treat the calculator as an estimate. If your months are hard to count, ask Social Security or check Medicare.gov.

The COBRA and retiree coverage trap

If you (or your spouse) have group health plan coverage based on current employment, you can delay Part B and use a Special Enrollment Period later. That period ends 8 months after the employment or the group health plan coverage ends, whichever comes first. Signing up during a qualifying Special Enrollment Period generally means no Part B late penalty.

The trap is assuming that other kinds of coverage count the same way. They do not:

• COBRA is not considered group health plan coverage based on current employment. Getting COBRA does not change when the 8-month Special Enrollment Period ends.
• Retiree coverage does not count as coverage from current employment.
• VA coverage and individual Marketplace plans do not count either.

The end of COBRA or retiree coverage does not qualify you for a Special Enrollment Period. The 8-month clock starts when the job or the employer coverage ends, not when COBRA ends. A person who keeps COBRA for a long stretch after leaving work can run out the clock and end up with a penalty.

If you are close to this situation, check your dates with Social Security or Medicare.gov before you decide to rely on COBRA.

Ways to avoid or end the penalty

Sign up during a Special Enrollment Period

If you delayed Part B because of coverage from current employment, enrolling within the 8-month window generally means no penalty.

Enroll in a Medicare Savings Program

Generally, there is no Part B late penalty if you enroll in a Medicare Savings Program, where your state pays your Part B premium. Whether you qualify depends on your situation, so check the official Medicare.gov information for details.

The reset at 65 for people on Medicare because of disability

If you have Medicare because of a disability and pay a Part B penalty, the penalty ends when you turn 65. Your premium goes back to the standard amount.

If you missed your window

If you miss your Initial Enrollment Period and do not qualify for a Special Enrollment Period, you can sign up during the General Enrollment Period, January 1 to March 31 each year. Coverage starts the month after you sign up, and a late penalty may apply.

Other than the exceptions above, there is no listed way to remove the penalty, so the best protection is knowing your dates before they pass.

FAQ

How much is the Part B late penalty in 2026?

It is 10% of the $202.90 standard premium for each full 12-month period you went without Part B when you could have had it. In Medicare.gov's example, a 24-month delay means a 20% penalty and a 2026 monthly premium of $243.50.

Does the Part B penalty ever go away?

Usually not. You generally pay it for as long as you have Part B. Exceptions include enrolling in a Medicare Savings Program, and people on Medicare because of a disability, whose penalty ends at 65.

Does COBRA let me delay Part B without a penalty?

No. COBRA does not count as coverage from current employment. It also does not extend the 8-month Special Enrollment Period, which starts when the job or the employer coverage ends.

If I missed my window, when can I sign up?

During the General Enrollment Period, January 1 to March 31. Coverage starts the month after you sign up, and a penalty may apply unless you qualify for a Special Enrollment Period.

Related guides

• Medicare Open Enrollment 2026 Dates: What You Can Change for 2027 Coverage

Sources

• Medicare.gov — Avoid late enrollment penalties
• Centers for Medicare & Medicaid Services (CMS) — 2026 Medicare Parts A & B Premiums and Deductibles
• Medicare.gov — When does Medicare coverage start?
• Social Security Administration (POMS HI 01001.010) — Premium Increase for Late Enrollment
• Social Security Administration — Understanding the Initial Enrollment Period and the Special Enrollment Period (Publication No. 05-10012)
• KFF — Is there any way to avoid the Part B late enrollment penalty?
• Medicare Rights Center (Medicare Interactive) — Part B late enrollment penalty

Facts last verified: 2026-10-11

This article is general health and benefits information drawn from the official sources listed above. It is not medical advice and does not replace a conversation with your doctor or pharmacist. Medicare and Social Security figures change every year; check the official site before you decide.