If you miss your initial enrollment window and go without required coverage for long enough, Medicare can add a late-enrollment penalty (LEP) to your monthly Part B and/or Part D premium. The LEP is not the same as IRMAA (an income-related surcharge): Medicare IRMAA basics. It is also not your Advantage plan’s out-of-pocket max: Medicare Advantage MOOP basics.
Official rules live on Medicare.gov and in Social Security / CMS publications. This page is orientation for budgeting—not an enrollment election.
Part B vs Part D penalty (plain map)
| Piece | Rough trigger (orientation) | How the add-on usually works |
|---|---|---|
| Part B LEP | Delayed Part B when you lack qualifying coverage / employer plan creditable setup past your initial enrollment period | Often 10% of the standard Part B premium for each full 12-month period you were eligible but not enrolled (paid as long as you have Part B—confirm current CMS wording) |
| Part D LEP | Gap of 63+ days without creditable prescription coverage after your initial Part D enrollment window | Often a % of the “national base beneficiary premium” × months without coverage, added to your Part D or MA-PD premium going forward |
Creditable coverage (many employer or union drug plans) can pause the Part D clock—get a written creditable-coverage notice from the plan, not a verbal “you’re fine.”
How LEP differs from nearby Medicare costs
- IRMAA scales with MAGI lookback; LEP scales with how long you waited. You can owe both.
- Medigap premiums are insurer prices for supplemental policies (What is Medigap); they do not erase a Part B LEP on the Medicare side.
- Part D coverage gap / “donut hole” language is about drug-stage cost sharing, not the LEP line item: Medicare Part D donut hole basics.
- Ordinary deductible vocabulary on non-Medicare plans still helps when you compare Advantage packages: Health insurance deductibles.
Worked example: Part B delay after leaving employer coverage
Jordan turns 65 in 2024, stays on a large-employer group plan with a working-spouse setup that delayed Part B appropriately, then retires July 2026 and waits until October 2028 to enroll in Part B during a general enrollment period after a long uncovered stretch. CMS counts full 12-month periods without Part B when Jordan should have had it. If that count is two such periods, a common illustration is a 20% Part B LEP (2 × 10%) on top of the standard Part B premium—for as long as Jordan keeps Part B.
Separately, if Jordan also lacked creditable drug coverage for more than 63 days, a Part D LEP can stack on the drug plan premium. Exact months and percentages belong on Jordan’s Medicare notice—not on a blog estimate.
Practical cues
- Mark your initial enrollment period and any special enrollment tied to job-based coverage ending.
- Keep creditable coverage letters for drug benefits each year you delay Part D.
- Budget LEP as a permanent-looking premium bump, not a one-month fee.
- Ignore cold callers who sell “LEP removal” for gift cards or wire—pay and appeal only through Social Security / Medicare.gov channels.
- Compare Advantage vs Original Medicare + Medigap on benefits and MOOP separately from whether an LEP already attaches to Part B.
Named institutions: Centers for Medicare & Medicaid Services (CMS), Social Security Administration, Medicare.gov, state SHIP counseling programs, and carriers (UnitedHealthcare, Humana, Aetna, Kaiser Permanente, Blues) that bill plan premiums beside any LEP Medicare collects.
Bill literacy after claims still sits in Medical bills and insurance.
Checklist
- Confirm whether you need Part B now or have a qualifying delay (employer coverage).
- Ask every drug plan for a creditable coverage determination in writing.
- Calendar 63-day Part D gaps if you leave creditable coverage.
- Read any LEP notice for which Part (B vs D) and how many months CMS counted.
- Budget Part B LEP + Part D LEP + IRMAA + plan premium as separate lines.
- Use SHIP / Medicare.gov for enrollment timing—not social DMs.
Medigap open enrollment timing is separate from Part B/D late-enrollment penalties: Medigap open enrollment basics.
Once enrolled, Part A inpatient costs follow benefit periods: Medicare Part A benefit period basics.
Educational only. Not insurance, tax, or legal advice. Not a plan recommendation. Late-enrollment penalty formulas, enrollment periods, and creditable-coverage rules change; confirm with Medicare.gov, Social Security, and a qualified counselor for your facts.