Delay Medicare Part B for 3 Years and a 30% Penalty Rides Every Premium for Life

A 66-year-old retires in early 2024, drops his employer plan, and signs up for COBRA to keep his old network for 18 months. He enrolls in Medicare Part B in mid-2026, two years after his group coverage ended. The Social Security letter that arrives a few weeks later says his Part B premium will carry a 20% surcharge. Permanently. He calls to argue: he had coverage the whole time. The answer he gets is the one nobody warned him about. COBRA does not count.

If you have active-employment group coverage right now, through your own job or a spouse’s, this article does not apply to you in the same way. You get a penalty-free Special Enrollment Period that runs for eight months after that employment ends. Everyone else, including anyone relying on COBRA, retiree coverage, marketplace plans, or no coverage at all, is on a hard clock the moment their Initial Enrollment Period closes.

The 10% Rule Rides A Moving Premium

The Part B late-enrollment penalty adds 10% of the standard premium for each full 12-month period you could have had Part B but did not. Three full years late is 30%. Four is 40%. The surcharge attaches to your premium for the rest of your life, and it recalculates every January against whatever the new standard premium is. It is a percentage of a moving number, not a fixed dollar bill.

That moving number is climbing. The standard Part B premium is $202.90 in 2026, up from $185.00 in 2025, and the Part B deductible jumped to $283. CPI-W, the index that drives Social Security and feeds into Medicare cost trends, sits at 328.829 as of May 2026, up from 315.945 a year earlier. The 2.8% Social Security COLA for 2026 is the kind of annual bump that keeps lifting the base your penalty rides on.

What A Three-Year Delay Actually Costs

Applied to the 2026 standard Part B premium of $202.90, a 30% late-enrollment penalty increases the monthly premium by about $60.87. That translates to roughly $730 in additional premium costs each year at current rates. Because the penalty is calculated as a percentage of the standard Part B premium, the dollar amount generally increases whenever Medicare premiums rise.

Over time, the additional cost can become significant. At today’s premium levels, a beneficiary paying an extra $730 per year for 20 years would spend about $14,600 in additional premiums. If Part B premiums continue to increase, the actual lifetime cost would be higher. The key point is that the penalty is not a one-time charge. It remains attached to the premium for as long as the beneficiary has Part B coverage.

The Exemptions, Stated Plainly

Two groups can delay Part B without owing a penalty:

• You are covered by a group health plan based on your own or your spouse’s current active employment. The 8-month Special Enrollment Period starts the month that employment ends or the coverage ends, whichever comes first.
• You qualify for an exceptional-conditions SEP, which is narrow and case-specific.

COBRA, retiree coverage, a spouse’s retiree plan, TRICARE for Life by itself, and ACA marketplace coverage are not considered active-employment coverage for purposes of the Part B Special Enrollment Period. If your employer coverage ended and you continued with one of these alternatives, the 8-month enrollment window generally began when the active-employment coverage ended, not when the replacement coverage began or expired.

Another common source of confusion is the Annual Enrollment Period, which runs from October 15 through December 7 each year. That window is primarily for changing Medicare Advantage and Part D prescription drug plans. It is not the standard enrollment period for someone signing up for Part B for the first time. Beneficiaries who miss both their Initial Enrollment Period and any applicable Special Enrollment Period generally must wait for the General Enrollment Period, which runs from January 1 through March 31, with coverage beginning after enrollment and potential late-enrollment penalties still applying.

What To Do This Week

• If your employer coverage already ended, count the months since that date. If you are still inside 8 months, file CMS-40B and CMS-L564 with Social Security now to lock in the SEP and avoid the penalty.
• If you are on COBRA or retiree coverage and over 65, stop treating that coverage as Medicare-equivalent. Enroll in Part B before the 8-month window from your active-employment end date closes.
• If a penalty has already been assessed and you believe Social Security misclassified your prior coverage, request reconsideration in writing and include proof of active-employment dates from your former employer’s HR office. The penalty is permanent if it sticks, so the appeal is worth the paperwork.

Figures reflect 2026 Medicare plan-year rules. Premium and deductible amounts from the CMS 2026 Medicare Parts A & B Premiums and Deductibles fact sheet.