A Surcharge for Life, Not a Fine You Pay Once
Most financial penalties are events: you pay them and they are over. Medicare's late enrollment penalties are different. They are added to your premium permanently, they rise every time the premium rises, and they are calculated from how long you delayed rather than from any harm caused. Two decades of a modest-sounding percentage adds up to a five-figure sum, and the people who incur it almost always believed they were covered.
- Part B:: 10% added to the standard premium for each full 12-month period you delayed, for as long as you have Part B.
- Part D:: A percentage of the national base premium for each month without creditable drug coverage, also permanent, and it rises as that base premium rises.
- Employer coverage can protect you:: Active employment coverage from a large employer generally lets you delay without penalty, and gives a special enrollment period when it ends.
- Two traps:: Retiree coverage and COBRA are not active employment coverage, and a small employer's plan may not protect you either. Both catch people who were genuinely insured.
Where the AI summary above gets this wrong
"If you are still working at 65 you can delay Medicare without any penalty."
That's surface-true. Here's what it misses:
- Only some employer coverage protects you — The exception depends on coverage from active employment, and for Part B generally on the employer being large enough. Someone working past 65 at a small employer may find Medicare is the primary payer and that delaying both leaves them underinsured and accruing a penalty.
- Retiree coverage and COBRA are not employment coverage — This is the commonest and most expensive misunderstanding. A retiree health plan or COBRA continuation feels like employer coverage and does not count for delaying Part B. People are covered, believe they are protected, and accrue a penalty for years without knowing.
- Part D catches people with no prescriptions — Someone taking no medication at 65 sees no reason to buy drug coverage, and the penalty accrues for every month without creditable coverage. By the time they need a plan, the surcharge is permanent and sized by how long they went without.
01 How each penalty is calculated
The Part B penalty adds 10% of the standard premium for each full 12-month period you were eligible and did not enrol. Delay three years and the premium is 30% higher — permanently, and recalculated upward each year as the standard premium rises. It is not a fixed dollar surcharge that inflation erodes; it is a percentage that grows with the thing it is applied to.
The Part D penalty works on months rather than years. It is a percentage of the national base beneficiary premium for each month you went without creditable prescription drug coverage, added to whatever plan you eventually choose, and likewise permanent.
Part A is different: most people have paid enough through employment to receive it premium-free, and where there is no premium there is no percentage to add. The penalties that matter in practice are B and D.
Source: Avoid late enrollment penalties
02 The coverage that actually protects you
The exception exists for people still working. Coverage from current active employment — yours or a spouse's — generally allows Part B to be delayed without penalty, and produces a special enrollment period when that employment or coverage ends.
Two conditions narrow it. The coverage must be from active employment, not from having once been employed. And for Part B the employer generally needs to be large enough; below that size Medicare becomes the primary payer at 65 whether or not you enrolled, which means declining it leaves real gaps as well as accruing a penalty.
This is where the expensive mistakes live. Retiree health coverage is not active employment coverage. Neither is COBRA. Both provide genuine insurance and neither protects you from the Part B penalty, so a household that retired at 63 with retiree coverage and delayed Medicare at 65 is accruing a surcharge while holding what feels like a full policy.
03 The arithmetic, and the enrollment window
A three-year delay adds 30% to the Part B premium. Over a twenty-year retirement, that is a five-figure sum on the premium alone, and it grows because the penalty is a percentage of a premium that rises most years.
The initial enrollment period runs for seven months around your 65th birthday — the three months before, the month itself, and the three after. Missing it without a qualifying exception means waiting for the general enrollment period, which both delays coverage and starts the penalty clock.
Two practical points. Claiming Social Security at or after 65 enrols you in Part A automatically, which has its own consequence for anyone still contributing to an HSA. And the penalty is separate from IRMAA — the income-related surcharge described in IRMAA surcharges — so a high-income household enrolling late can carry both at once, one for their income and one for their timing.
Shows: what a Part B late enrollment penalty costs over the rest of your life, since the surcharge is permanent rather than a one-off. Ignores: future premium increases, which raise the penalty with them, and any exception that would waive it.
Source: Medicare costs
Almost everyone I have seen pay this was insured the whole time. They retired early, kept retiree coverage or took COBRA, and reasonably concluded that having health insurance meant they could delay Medicare. Nobody tells you those do not count, and nothing arrives to warn you while the clock runs. If you are approaching 65 and not actively employed, the question worth asking out loud is not whether you have coverage but whether it comes from a job somebody is currently doing. That is the whole distinction, and it is worth a phone call rather than an assumption.
FAQ
How much is the Medicare Part B late enrollment penalty?
10% of the standard premium for each full 12-month period you were eligible and did not enrol, added permanently. A three-year delay means a 30% higher premium for as long as you have Part B, rising each time the standard premium does.
Does working past 65 let me delay Medicare?
Generally yes, if you have coverage through current active employment and, for Part B, the employer is large enough. When that employment or coverage ends you get a special enrollment period. Retiree coverage and COBRA do not count as active employment coverage.
I take no medications — do I still need Part D?
Without creditable drug coverage the Part D penalty accrues for every month you go without, and it is permanent once it applies. Taking no prescriptions at 65 is the commonest reason people skip it, and the surcharge is sized by exactly how long they waited.
Sources
Regulator references
- Avoid late enrollment penalties · Centers for Medicare & Medicaid Services · 2026Which parts carry a late enrollment penalty and how each is calculated.Last verified: 2026-09-07
- Medicare costs · Centers for Medicare & Medicaid Services · 2026The premiums the penalty is applied as a percentage of.Last verified: 2026-09-07
- When does Medicare coverage start · Centers for Medicare & Medicaid Services · 2026Enrollment periods, and when coverage begins once you sign up.Last verified: 2026-09-07
Calculator unit tests · the assertions this page's worked example is checked against, and their last result
Changelog
- 2026-09-07 — initial publish (new format)
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Jordan Reeves
Founder of Talk Through Wealth. A software engineer for over a decade before turning to retirement planning, Jordan built the projection engine after watching family members get fragmented, country-by-country advice that never reconciled. He writes about retirement the way the engine computes it: month-by-month, lifetime-long, and skeptical of any rule of thumb that hasn't been run through the math.