Medicare late enrollment penalties
Signing up late adds a surcharge to the Medicare premium, and it is usually permanent. There are two, they are calculated differently, and one person can pay both. Every figure below comes from the statute or from CMS, with the document named.
Part B and Part D, side by side
| Part B | Part D | |
|---|---|---|
| Rate | 10% per full 12 months | 1% per uncovered month |
| Calculated on | the standard premium, $202.90 in 2026 | the national base beneficiary premium, $38.99 in 2026 |
| Behaviour | Steps. Eleven months late is no penalty at all. | Accrues. Every single month counts. |
| Two years late | $40.58 a month | $9.40 a month |
| Rounding | none stated | to the nearest $0.10, once |
| Source | 42 U.S.C. § 1395r(b) | 42 CFR 423.286 |
The same two-year delay costs different amounts under each rule because the bases differ. Work either out for your own month count with the calculators on the pages below.
The Part B penalty
10% for each full 12 months, so it steps rather than accrues — eleven uncovered months is nothing, twenty-three is one step, twenty-four is two. The months excluded are the ones covered by a group health plan through current employment, and proving those is what Form CMS-L564 is for.
A high income does not raise it. 42 U.S.C. § 1395r(b) computes the increase on the premium “without regard to any adjustment under subsection (i)” — and subsection (i) is IRMAA. Most pages state the penalty as a percentage of “the standard premium” without saying why. That is why.
Form CMS-L564 and the Part B penalty has the statute quoted in full, a calculator, the 8-month Special Enrollment Period clock, and which months count.
The Part D penalty
1% of the national base beneficiary premium for each full month without Part D or other creditable drug coverage, rounded once to the nearest $0.10. It is triggered by a continuous gap of 63 days or more after the Initial Enrollment Period, not by any gap.
The regulation says something the consumer pages do not. 42 CFR 423.286(d)(3) makes the penalty the greater of an actuarially sound amount CMS determines or that 1% figure. Every consumer page publishes only the 1%, which is a floor presented as a definition.
The Part D late enrollment penalty has the calculator, the base premium for every year CMS has published it, the creditable-coverage rules, and the clause that lets someone who was never told their coverage was not creditable ask CMS to treat it as though it were.
What we have not published
Most people pay no Part A premium, so no Part A late enrollment penalty arises. For those who do buy in, a penalty exists — but we have not verified its rule against a primary source, so there is no figure for it here. The statute does not state a rounding rule for the resulting amount, and does not say the penalty is permanent in so many words - it states an increase to the monthly premium. Neither CMS-L564 nor CMS-40B states a rounding rule either. We therefore publish the percentage, not a rounded dollar figure. Why we work this way.
How these differ from IRMAA
IRMAA is a surcharge based on income from two years ago. These penalties are surcharges based on when someone signed up. All three land on the same monthly bill, and one person can pay all of them, but none multiplies another.
At the other end of the income range, the Medicare Savings Programs pay the Part B premium outright for those who qualify — QMB also covers deductibles and coinsurance, while SLMB and QI cover the premium at higher income bands. Qualifying for any of them is also a route to Extra Help, which is the published exception to the Part D penalty.
Published rules with the statute or CMS document named for each. It is not advice and not a determination — Social Security decides enrollment and premiums. For help with an individual situation, Social Security is on 1-800-772-1213 and a State Health Insurance Assistance Program counsellor is free at shiphelp.org.