Medicare late enrollment penalty calculator to estimate Part B or Part D penalties from uncovered months, base premiums, plan cost, and expected payment years.
Medicare Late Enrollment Penalty Formula
The standard Part B late enrollment penalty increases the monthly premium by 10% for each full 12-month period a person could have had Part B but did not enroll, subject to exceptions:
Part B Monthly Penalty = Part B Premium * 10% * Full 12-Month Periods
The standard Part D penalty uses 1% of the national base beneficiary premium for each uncovered month and rounds the result to the nearest $0.10:
Part D Monthly Penalty = round_to_$0.10(Base Beneficiary Premium * 1% * Uncovered Months)
Variables:
- Part B Premium is the standard monthly premium, excluding IRMAA and other adjustments
- Full 12-Month Periods is the number of complete 12-month periods in the countable Part B months after the Initial Enrollment Period, excluding qualifying protected months
- Base Beneficiary Premium is the national Part D base for the applicable year
- Uncovered Months is the count of qualifying months without Part D or creditable drug coverage
The default inputs reflect 2026 amounts: $202.90 for the standard Part B premium and $38.99 for the Part D national base beneficiary premium. Both are editable because amounts can change.
Medicare Penalty Examples
The table uses the editable 2026 default base amounts and assumes no exception or special enrollment period applies. Part B amounts are unrounded formula penalties; Part D amounts are rounded monthly penalties.
| Coverage | Delay | Penalty rate or months | Estimated monthly penalty |
|---|---|---|---|
| Part B | 11 months | 0 full 12-month periods | $0.00 |
| Part B | 30 months | 20% | $40.58 |
| Part B | 49 months | 40% | $81.16 |
| Part D | 18 uncovered months | 18 months | $7.00 |
Example Problems
Example 1: Calculate a Part B penalty.
A person delayed Part B for 30 months without an applicable exception. That contains two full 12-month periods.
Using the $202.90 standard premium, the unrounded formula penalty is $202.90 × 20% = $40.58 per month. The combined premium is $243.48 before rounding and $243.50 after rounding the total to the nearest $0.10. Annual and cumulative Part B formula estimates use the unrounded penalty, so they can differ from the increase in billed premiums. Cumulative estimates hold the current amount fixed; future premiums can change.
Example 2: Calculate a Part D penalty.
A person had 18 qualifying uncovered months and the base beneficiary premium is $38.99.
The unrounded penalty is $38.99 × 1% × 18 = $7.0182, which rounds to $7.00 per month.
Frequently Asked Questions
Does every delay cause a Medicare penalty?
No. Current employment coverage, special enrollment periods, creditable prescription coverage, and other exceptions can prevent a penalty. Confirm the official determination with Medicare or Social Security.
How long do Medicare late enrollment penalties last?
Standard Part B and Part D penalties can generally continue while the person has that coverage, though specific programs and circumstances can change the duration.
Why can a Part D penalty change each year?
The uncovered-month count generally remains fixed, but the national base beneficiary premium can change annually. The dollar penalty is recalculated from that year’s base.
Coverage-year check, October 20, 2026: the calculator keeps 2026 defaults. CMS has published a 2027 Part D national base beneficiary premium of $41.33; enter $41.33 to estimate a 2027 Part D penalty. This is not a quoted plan premium and does not set the 2027 Part B premium. Sources: 2026 Part B premiums and CMS Part D creditable-coverage and penalty guidance.
