The Part B penalty: 10% per year late, for life

The exact math, worked

Penalty percentages applied to the 2026 standard premium of $202.90. The percentage is fixed; the dollar amount rises with each year’s premium.

Correction to a common misreading of that table: the "extra paid per year" column compounds across a lifetime. A 67-year-old who was two years late and lives to 87 pays the 20% surcharge for 20 years; at today’s premium alone that’s roughly $9,700, and since the base premium historically rises most years, the true lifetime figure runs meaningfully higher. The penalty is calculated in full 12-month periods, which creates one merciful rounding rule: eleven months late rounds to zero periods, no penalty. Twelve full months is where the meter starts.

Who’s protected, who isn’t

• Fully protected: people covered by a group health plan from their own or their spouse’s current employment at an employer with 20+ employees. Delay as long as that lasts; an 8-month Special Enrollment Period opens when it ends, penalty-free.
• Not protected, despite feeling like coverage: COBRA, retiree health plans, severance-package coverage, VA health care, and ACA marketplace plans. All are real insurance; none stops the penalty clock. The COBRA case fills more regret threads than any other single Medicare mistake.
• Also protected: people who enroll during their Initial Enrollment Period, obviously, and those with Medicaid (different rules apply).

The proof that protects you is paperwork: when you eventually enroll after workplace coverage, Social Security asks for form CMS-L564, completed by the employer, attesting to the coverage dates. Get it signed while the HR department still knows you; chasing a defunct employer’s records years later is its own genre of misery.

The second cost: waiting for the door to open

Miss your window without protection and you can’t simply enroll whenever regret arrives: you wait for the General Enrollment Period, January 1–March 31, with coverage starting the month after you sign up. Someone who realizes in April therefore waits nine-plus months for coverage to even begin, uninsured against 100% of outpatient costs the whole time. The penalty gets the headlines; the coverage gap does the acute damage.

The narrow escape routes

• Prove the coverage existed. Many "penalties" are documentation failures: the L564 form or employer letters showing qualifying coverage erase the periods they cover.
• Equitable relief. If a federal employee’s error or misinformation (Social Security, Medicare) caused the delay, you can request relief in writing with the specifics; it’s granted more often than folklore suggests, and never granted to people who don’t ask.
• Special situations: certain Medicaid-to-Medicare transitions and disaster/emergency SEPs added in recent years can reopen enrollment without penalty. A free SHIP counselor can match your facts to the current SEP list.
• What doesn’t work: "I didn’t know" (not relief), "I was healthy" (not relief), and "my agent said" (only federal misinformation counts).

The sibling penalty, briefly

Part D runs its own meter: 1% of the national base premium ($38.99 in 2026) per month without creditable drug coverage, also permanent. Sixty-three days is the grace period after losing creditable coverage. The two penalties travel together in most missed-enrollment stories, which is why the fix is identical: enroll on time, or hold documented qualifying coverage, with the dates provable. Prevention costs nothing; the alternative costs monthly, forever.

Questions people also ask

Sources for this article

• SSA.govSign up for Medicare: enrollment periods, penalties, and the employment-coverage exception.
• Medicare.govMedicare.gov: General Enrollment Period timing and penalty rules.
• CMS.gov2026 premiums and deductibles: the $202.90 base the percentages apply to.

Figures checked against these sources in August 2026. We update within weeks when CMS publishes new amounts.