Medicare late enrollment penalty calculator (Part B and D)

By the Deorbit Plan editorial team, a Berrydyne program · Last reviewed November 2026 · Topic: Medicare & IRMAA

What it computes

Miss your Medicare enrollment window without other qualifying coverage and the premium goes up for life. Part B adds 10% of the standard premium for each full 12-month period you went without it; Part D adds 1% of the national base beneficiary premium for each full month without creditable drug coverage, once the gap passes 63 days^[1]. Enter the number of uncovered months and the calculator applies both rules to the 2026 premiums ($202.90 Part B, $38.99 Part D base)^[4]^[1].

Estimate your penalty (2026 premiums)

Full months without coverage after your enrollment window closed

Part B: 20% penalty. About $40.58/month extra, so $243.50/month instead of the $202.90 standard premium, before any IRMAA surcharge.
Part D: 24% penalty. About $9.40/month added to whatever your plan charges (24% of the $38.99 national base premium).

The percentages are permanent; the dollar amounts are recomputed against each year’s premiums, so they grow over time. Part D’s meter only starts once you are 63+ days past your window, and months covered by employer or other creditable coverage don’t count for either penalty.

Worked example

Enrolling 24 months late means 2 full years without Part B: a 20% penalty, so the $202.90 standard premium becomes $243.50 a month. The same gap without drug coverage is a 24% Part D penalty, about $9.40 a month on top of the plan premium^[1].

Monthly penalties at 2026 premiums by length of the gap
Uncovered months	Part B penalty	Part B premium	Part D penalty
12	10%	$223.20	12% ($4.70)
24	20%	$243.50	24% ($9.40)
36	30%	$263.80	36% ($14.00)
60	50%	$304.40	60% ($23.40)

The percentages never expire; the dollar amounts are recomputed on each year’s premiums, so they grow over time.

What it ignores

Whether your months were actually uncovered: employer coverage from current work (yours or a spouse’s) and creditable drug coverage stop the clock^[5].
Special Enrollment Periods and the programs that remove the penalty for some people^[2]^[1].
The Part A penalty for people who must buy Part A^[3].
IRMAA, the separate income-based surcharge on Parts B and D.

The rule behind it

The full explanation, with sources, is in Medicare Part B late enrollment penalty calculator (and Part D).

See it over a full plan

The simulator assumes on-time enrollment at 65 and prices the years before it on the ACA marketplace. That handoff is where late-enrollment mistakes happen. Open it in the simulator →

If you already have a saved plan, the link only takes you to the right panel; your plan is not changed.

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Medicare late-enrollment penalty calculator