Medicare late enrollment penalty calculator
Part B, Part D and Part A: what waiting costs you each month.
Amounts are examples — use your own. Count only months Medicare would count; a Special Enrollment Period or Extra Help can remove the penalty.
How is the Part B late enrollment penalty figured?
For each full 12-month period that you could have signed up for Part B but did not, you pay an extra 10% of the standard premium. Medicare.gov gives the example that 24 months late means a 20% penalty. In 2026, with a standard premium of $202.90, that is $40.58 a month.
Does 23 months count as one year?
Yes, only full 12-month periods count. A person who waited 23 months pays 10% ($20.29 a month in 2026), and the second 10% starts only after month 24.
Is the Part B penalty permanent?
For most people, yes. Medicare.gov says you usually pay it as long as you have Part B, and because it is a percentage of the standard premium, it grows when the premium grows.
When is there no penalty?
Generally if you qualify for a Special Enrollment Period (for example if you or your spouse kept working and had group health coverage through an employer) or if you enroll in a Medicare Savings Program. Check the details on Medicare.gov before you decide not to enroll.
How is the Part D penalty figured in 2026?
1% of the national base beneficiary premium ($38.99 in 2026) times the number of full months you went without creditable drug coverage after your initial enrollment period, rounded to the nearest 10 cents. Medicare.gov’s example of 14 months comes to a 14% penalty, about $5.50 a month.
What is a gap in creditable coverage?
The penalty applies if you go 63 days or more in a row without Part D or other drug coverage that is at least as good as Medicare’s standard coverage. Extra Help recipients are generally excluded.
Is there a Part A penalty?
Only for people who must buy Part A, which about 99% of people do not (they have at least 40 quarters of work). If you buy it and did not sign up when first eligible, the monthly premium may go up 10%, and you pay the higher amount for twice the number of years you did not sign up.
What the number means
Medicare’s late enrollment penalties are meant to make people sign up when they are first eligible. They are added to the monthly premium, so they work like a permanent surcharge. The three parts use three different rules, so the calculator has a button for each. All amounts are for 2026.
The three formulas
Part B: penalty = $202.90 × 10% × the number of full 12-month periods without Part B after you were first eligible. The penalty is added to the standard premium; it does not change with your income, and IRMAA is added separately. Part D: penalty = 1% × $38.99 × the number of full months without creditable drug coverage, rounded to the nearest $0.10. Part A (if you pay a premium): penalty = 10% × the Part A premium ($565.00 a month for people with fewer than 30 quarters of work, $311.00 for 30 to 39 quarters), charged for twice as many years as you were late.
Worked example: Part B, 24 months late
Someone who enrolled in Part B 24 months after the end of the first eligibility period has two full 12-month periods, a 20% penalty. In 2026 that is $202.90 × 20% = $40.58 a month on top of the $202.90 premium, so $243.48 a month, or $486.96 extra a year. Someone five years late (60 months) pays 50%: $101.45 a month, $1,217.40 a year, nearly $24,348.00 over 20 years even if the premium stayed flat. For Part D, 36 uncovered months give a 36% penalty, $14.04 before rounding and $14.00 after it. For a Part A premium payer who is 24 months late, the penalty is $56.50 a month for 4 years, about $2,712.00 in total.
Common mistakes
Thinking that a penalty is a one-time fee: Part B and Part D penalties continue for as long as you are enrolled, and they are recalculated whenever the premium changes. Counting months while you had employer coverage based on current work: those months generally fall under a Special Enrollment Period and do not count, though retiree coverage and COBRA usually do not qualify. Counting a Part D gap from the day you turned 65: the clock runs from the end of your initial enrollment period, and a gap of fewer than 63 days is not penalized. Forgetting that the Part B penalty is a percentage of the standard premium, not of your actual premium, so higher-income surcharges do not make it larger.
Limits of this method
You enter the number of late months yourself, because Social Security or Medicare decides which months count and whether an exception applies. The calculator does not decide whether you are eligible for a Special Enrollment Period, Extra Help or a Medicare Savings Program, all of which can remove or lower a penalty. The Part B annual amounts assume the 2026 premium; real premiums rise most years, and the penalty rises with them. The Part B penalty may differ by a few cents from the amount on your bill because of rounding.
An estimate for planning only — not financial advice; Medicare and Social Security decide your penalty. Sources, checked October 28, 2026: Medicare.gov, How to avoid Medicare penalties and Part D late enrollment penalty; CMS fact sheet 2026 Medicare Parts A & B Premiums and Deductibles (standard Part B premium and Part A premiums). Related: Medicare IRMAA calculator, Social Security calculator, retirement calculator, earnings test calculator and RMD calculator. How we check our calculators.