Medicare Part B Late Enrollment Penalty Calculator
Enter your client's date of birth and when their Part B coverage starts. We work out the enrollment period, the uncovered months, and what the penalty really costs — monthly, yearly, and over a lifetime.
Nothing you enter leaves your browser — every calculation runs on your device
Client details
Type straight through — no tabbing. Pasting works too.
Use the next General Enrollment Period date if unsure.
Projection assumptions
An assumption — adjust to your client.
The penalty is a percentage of a premium that rises each year.
Result
Enter a date of birth and a Part B start date to see the estimate.
Estimate only, based on CY2026 figures (standard Part B premium $202.90). This is not an official determination. MedicareCopilot is not affiliated with or endorsed by CMS, Medicare, the Social Security Administration, or any government agency — official amounts and eligibility determinations are made by SSA and CMS. This tool provides general information only and is not medical, legal, or tax advice. Figures last verified 2026-07-27.
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How the Part B late enrollment penalty works
The Medicare Part B late enrollment penalty is 10% of the standard Part B premium for each full 12-month period you could have had Part B but didn't. In 2026 the standard premium is $202.90, so each full year of delay adds about $20.30 per month.
Only complete 12-month periods count. Someone who enrolled 11 months late owes nothing; someone 23 months late owes one period's worth, not two.
The penalty lasts for as long as you have Part B, and because it is a percentage of a premium that CMS resets every year, the dollar amount grows over time. It is charged on top of the standard premium, and any income-related adjustment (IRMAA) is added separately.
You can avoid the penalty entirely if you had group health coverage through active employment at an employer with 20 or more employees. That opens an 8-month Special Enrollment Period beginning when the employment or the coverage ends, whichever comes first. COBRA, retiree coverage, and severance benefits do not qualify.
Common questions
How much is the Medicare Part B late enrollment penalty?
The Part B late enrollment penalty is 10% of the standard Part B premium for each full 12-month period you could have had Part B but did not. In 2026 the standard premium is $202.90, so one full year of delay adds about $20.30 per month and two full years adds about $40.60 per month.
The amount is rounded to the nearest $0.10 and added to your monthly premium.
How long do you pay the Part B penalty?
You pay the Part B late enrollment penalty for as long as you have Part B — in practice, for life.
Because the penalty is a percentage of the standard premium and that premium is reset every year, the dollar amount you pay generally increases each year rather than staying fixed.
Does employer coverage let me delay Part B without a penalty?
Only if the coverage comes from active employment at an employer with 20 or more employees. That gives you an 8-month Special Enrollment Period starting when the employment or the group health coverage ends, whichever comes first.
If the employer has fewer than 20 employees, Medicare is the primary payer and you generally need to enrol at 65 even if you keep the employer plan.
Does COBRA count for Medicare Part B?
No. COBRA, retiree coverage, and severance health benefits do not qualify for the Part B Special Enrollment Period.
The 8-month window runs from the end of active employment, not from the end of COBRA. Waiting for COBRA to run out before enrolling in Part B is one of the most common and most expensive Medicare mistakes.
When can I enrol if I missed my Initial Enrollment Period?
The General Enrollment Period runs January 1 through March 31 each year. Coverage begins the first of the month after you sign up.
That is a change worth noting: before 2023 coverage did not begin until July 1, and many agents and beneficiaries still believe that is the rule.
Is the penalty based on my actual premium or the standard premium?
The penalty is calculated on the standard Part B premium, not on what you personally pay.
If you pay an income-related monthly adjustment amount (IRMAA), that is added separately and does not increase the penalty.
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