This site is not affiliated with or endorsed by the U.S. government or the federal Medicare program. It is a free educational calculator. Always confirm your dates with the official sources at Medicare.gov and the Social Security Administration.

Part B adds 10% for each FULL 12-month period you were late. Part D adds 1% for every full uncovered month. The difference matters: an 11-month Part B gap costs nothing, while the same gap does create a Part D penalty. Both are permanent surcharges on your monthly premium.

Medicare Late-Enrollment Penalty Calculator

Estimate the Part B and Part D late-enrollment penalties from how many months you went without coverage. Both are permanent surcharges added to your monthly premium for as long as you hold the coverage.

Why the two penalties behave so differently

Medicare's two late-enrollment penalties are often described together, which hides the single most useful difference between them. Part B counts only complete 12-month periods. Part D counts every full month. That asymmetry produces results that surprise people in both directions.

Go eleven months without Part B and the penalty is zero — not reduced, zero. Go twelve and it becomes 10% of the standard premium, permanently. Meanwhile those same eleven months without creditable drug coverage do generate a Part D penalty, because Part D has no such grace. Someone who delayed briefly and assumes they are safe on both counts is usually wrong about Part D; someone who delayed briefly and panics about Part B is usually wrong about Part B.

The other thing worth internalising is duration. Neither penalty is a one-time charge. They ride on your premium for as long as you hold the coverage, which for most people means the rest of their life. A surcharge of about fifty dollars a month reads as small; the same surcharge across twenty years of coverage is roughly twelve thousand dollars. That is why the calculator shows the monthly, annual, and horizon figures together rather than just the monthly one.

The formulas

  • Part B: 10% × (full 12-month periods late) × the standard Part B premium. At the 2026 premium of $202.90, one full year late is about $20.29 per month.
  • Part D: 1% × (full uncovered months) × the national base beneficiary premium, rounded to the nearest $0.10. At the 2026 base of $38.99, twelve uncovered months is about $4.68 per month.

Both figures move over time, because both are percentages of premiums that are set annually. The Part D penalty in particular is recalculated each year against the new national base beneficiary premium, so a penalty quoted this year is not the amount you will pay in five years. The lifetime figure here holds today's rates constant, which makes it a floor rather than a forecast.

What this page cannot do: it cannot tell you whether a Special Enrollment Period covers your gap, whether a former employer's drug plan was creditable, or whether your circumstances support a reconsideration. Those depend on your records and on Medicare's determination, not on arithmetic.

Worked examples

Medicare penalty questions, answered

How is the Medicare Part B late-enrollment penalty calculated?
The Part B penalty adds 10% of the standard Part B premium for each FULL 12-month period you could have had Part B but did not sign up. Crucially, it counts only complete 12-month periods: a delay of 11 months adds nothing at all, while a delay of 12 months adds 10%. Using the 2026 standard premium of $202.90, two full years late works out to about $40.58 extra per month. The surcharge is added to your premium for as long as you have Part B.
How is the Part D penalty different?
Part D counts every full month, not full years, which is why a short gap can produce a Part D penalty but no Part B penalty. It adds 1% of the national base beneficiary premium for each full month you were 65 or older without creditable prescription drug coverage, rounded to the nearest 10 cents. With a 2026 national base premium of $38.99, 24 uncovered months is roughly $9.36 a month.
How long do these penalties last?
Generally for as long as you hold the coverage — that is what makes them expensive. They are not one-off charges you settle and forget. Because they are calculated as a percentage of premiums that change annually, the dollar amount drifts each year: the Part D penalty is recalculated against the new national base beneficiary premium, and the Part B penalty moves with the standard premium. That is why this calculator also shows an annual and a lifetime figure, which is the number people underestimate most.
What is creditable drug coverage?
Coverage that is expected to pay, on average, at least as much as standard Medicare prescription drug coverage — typically an employer or union plan, or certain retiree and veterans' coverage. Months covered by a creditable plan do not count toward the Part D penalty. Your plan is required to tell you each year whether its coverage is creditable, so keep those notices: they are the evidence that a gap should not be counted against you.
Can a late-enrollment penalty be avoided or removed?
Sometimes. If you delayed because you had employer coverage through your own or a spouse's active employment, a Special Enrollment Period may let you enroll without a penalty, which is why this calculator asks for months you could have enrolled and were not otherwise protected. There are also limited circumstances in which a penalty can be reconsidered. Because both depend on your specific record, confirm with Medicare.gov or the Social Security Administration rather than assuming from a calculator.
Are these figures official?
No. They are estimates produced from the published penalty formulas and the 2026 premium figures, for planning only. This site is not affiliated with the U.S. government or the Medicare program, and this page is not advice or a determination of what you owe. Only Medicare and the Social Security Administration can tell you your actual penalty.

Understand the deadlines that cause penalties