Medicare Part B carries a penalty structure most people never look at until it already applies to them: for every full 12-month period someone was eligible for Part B but did not sign up, and had no other qualifying coverage, 10 percent gets permanently added to the monthly premium. The penalty is not a one-time fee and it does not expire after a few years. It rides along with the Part B premium for as long as a person keeps the coverage, which for most beneficiaries means the rest of their life.
How The 10 Percent Penalty Accumulates
The math is straightforward but unforgiving. Someone who delays enrollment by 24 full months owes a 20 percent penalty, 10 percent for each of the two 12-month periods, added on top of whatever the standard Part B premium happens to be that year. Wait five years instead of two, and the surcharge compounds to 50 percent of the premium, permanently, with no cap written into the rule.
Applied to the $202.90 standard Part B premium set for 2026, a 20 percent penalty adds roughly $40 a month, pushing the bill to about $243.50 every month, for as long as the person stays enrolled in Part B, unless the underlying standard premium itself changes with a new year’s update.
Because the penalty is based on full 12-month periods rather than partial ones, timing matters. Someone who waits 13 months instead of 11 crosses into a second full year and owes a second 10 percent, even though the delay only grew by two months. The dollar amount of the penalty is recalculated whenever the standard premium changes, so it keeps growing even after the percentage itself stops moving.
The penalty follows a beneficiary even into Medicare Advantage. Someone who enrolls in a Medicare Advantage plan instead of staying on Original Medicare still has to keep paying Part B, along with any separate plan premium, because Medicare Advantage is built on top of Part A and Part B rather than replacing them. Skipping Part B to save money during that window is not an option once the enrollment period has passed without another qualifying reason.
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The Enrollment Windows That Avoid It
The penalty exists to encourage people to sign up during one of two windows. The Initial Enrollment Period runs seven months around a person’s 65th birthday, three months before, the birth month, and three months after, and anyone who enrolls then owes nothing extra regardless of when they actually start using Part B.
A second window, the General Enrollment Period, runs January 1 through March 31 each year for anyone who missed their Initial Enrollment Period and does not qualify for a special exception. Signing up there stops further penalty growth going forward, but it does not erase whatever penalty already accrued for the months or years already missed.
The late-enrollment penalty is separate from, and can be stacked with, the income-related surcharge higher earners pay on the same Part B premium. A retiree who both delayed enrollment and reports income above the surcharge threshold pays both amounts on top of the standard premium, not one or the other, since the two calculations run independently and neither one offsets the other.
Two Ways The Penalty Can Be Skipped
Two circumstances let someone sign up late with no penalty at all. The first is an 8-month Special Enrollment Period tied to active employment: someone covered by a current employer’s group health plan, or a spouse’s, can wait until that coverage or the job itself ends and still enroll penalty-free within eight months. The second is enrollment in a Medicare Savings Program, which waives the Part B penalty entirely regardless of how long the person went without coverage.
COBRA and retiree health coverage do not count as active employment for this purpose. Someone who leaves a job and switches to COBRA still starts the 8-month clock the day the employment itself ends, not when COBRA eventually runs out, a distinction that has caught people who assumed COBRA bought them more time and delayed enrolling until the COBRA period itself ran out, well past the actual eight-month deadline tied to the job.
The rule rewards specific proof: an employer generally has to certify the group coverage on Medicare’s own form when a beneficiary later enrolls under the Special Enrollment Period, so keeping that paperwork from an employer’s human resources department at the time coverage ends can prevent a drawn-out penalty dispute years afterward, when pay stubs and benefit letters are much harder to track down.
The Programs Under The Same Roof
A Part B penalty this permanent is exactly the kind of cost a Medicare Savings Program is built to erase, since qualifying for one waives the penalty and picks up the premium itself going forward. The two rules sit on opposite ends of the same Part B bill, one punishes a missed deadline, the other forgives it for people under an income limit.
A 69-page guide walks through all 11 programs that can lower a Medicare or retirement bill, including the 2026 income cutoffs for Medicare Savings Programs and a 50-state phone directory for where to apply.
Look up The Benefits Checklist to see which of those programs might apply.
This article was researched and drafted with AI assistance and reviewed against primary sources before publication.
