Part D Late-Enrollment Penalty Calculator
The Medicare Part D late-enrollment penalty is 1% for every full month you went without creditable drug coverage. The count starts when your Initial Enrollment Period ends. The 1% is taken from the national base beneficiary premium, which is $38.99 in 2026. Medicare adds the result to your drug plan premium and works it out again each year.
This page estimates the Part D late-enrollment penalty — the one charged for going without drug coverage. Pick how long the gap lasted, in years and months, and it applies Medicare's rule: one percent of the national base beneficiary premium ($38.99) for every full uncovered month. You get the percentage, the amount added to your monthly drug premium, and what that comes to over a year.
It differs from the Part B penalty in kind: Part B counts whole twelve-month periods at ten percent each, where Part D counts every full month at one percent. The page itself notes only that Part B works differently, and links to that calculator. The percentage stays for as long as you have drug coverage, and because it is recalculated against each year's base premium, the amount rises when that premium does.
All it needs is the length of the gap — nothing personal is collected to run it, though optional forms below can request a call or an email course.
Two things can shrink the result or erase it. Months covered by an employer or union plan, VA benefits or TRICARE are creditable and are not penalty months — your plan tells you each year whether its coverage counts. And people who qualify for Extra Help pay no Part D late-enrollment penalty at all. A gap shorter than 63 days carries none either.
It is an estimate. Your plan and Social Security set the real amount, and the page does not enroll you or price a drug plan.
Frequently asked questions
How is the Part D late-enrollment penalty calculated?
Medicare counts every full month you went without creditable drug coverage. It charges 1% of the national base beneficiary premium for each of those months. The total is rounded to the nearest ten cents and added to your plan's premium.
Which drug coverage counts as creditable?
Coverage that pays, on average, at least as much as standard Part D. That commonly means an employer or union plan, VA benefits or TRICARE. Your plan must tell you in writing each year whether its coverage is creditable.
Can the Part D penalty be avoided or removed?
In two situations. People who qualify for Extra Help pay no Part D late-enrollment penalty. And a gap shorter than 63 days in a row carries no penalty at all.
Is the Part D penalty the same as the Part B penalty?
No. Part D charges 1% of the national base premium for each full uncovered month. Part B charges 10% of the standard premium for each full 12-month period. The two are counted separately.
Updated September 8, 2026. Dollar figures are 2026 plan-year amounts transcribed from CMS publications and last verified by IM65 against the source for each: Part D costs (October 1, 2026).