If you don’t sign up for Medicare at 65, you could face permanent penalty surcharges on your monthly premiums, gaps in health coverage that last months, and unexpected tax complications if you have a Health Savings Account. The consequences depend on which parts of Medicare you delay and whether you have qualifying coverage through an employer.
Your Initial Enrollment Window
Medicare gives you a seven-month window to sign up, starting three months before the month you turn 65 and ending three months after it. This is called the Initial Enrollment Period. If you miss it without qualifying coverage elsewhere, you enter penalty territory for Parts B and D, and you may have to wait months before you can enroll at all.
The Part B Late Enrollment Penalty
Part B covers doctor visits, outpatient care, and medical services. If you miss your initial window and don’t have qualifying employer coverage, your Part B premium increases by 10% for every full 12-month period you were eligible but didn’t enroll. That penalty is permanent. It gets added to your premium for as long as you have Medicare.
So if you waited two full years past your eligibility, you’d pay 20% more every month for the rest of your life. At current premium levels, that adds up to hundreds of dollars a year in extra costs that never go away.
The Part D Late Enrollment Penalty
Part D covers prescription drugs. If you go 63 days or more without creditable drug coverage after your initial enrollment period ends, you’ll owe a penalty of 1% of the national base beneficiary premium for every month you were uncovered. In 2026, that base premium is $38.99. Like the Part B penalty, this surcharge is permanent and gets recalculated each year as the base premium changes.
For example, if you went without drug coverage for 18 months, your penalty would be 18% of $38.99, or roughly $7 extra per month. That number adjusts annually as the base premium rises, so the actual dollar amount you pay tends to increase over time.
Coverage Gaps Between Enrollment Periods
Missing your initial window doesn’t just cost you money in penalties. It also leaves you without coverage for a stretch. If you miss the seven-month Initial Enrollment Period, your next chance to sign up is during the General Enrollment Period, which runs from January 1 through March 31 each year. Coverage then starts the month after you enroll.
Depending on when you turned 65 and how long you waited, this gap could be several months or longer. During that time, you’re responsible for the full cost of any medical care or prescriptions out of pocket.
When Employer Coverage Protects You
The penalties don’t apply if you have creditable coverage through an employer. But not just any employer plan qualifies. The employer must have 20 or more employees, and the coverage must be through your own active employment or your spouse’s. If those conditions are met, you can delay Medicare enrollment without penalty.
Once that employer coverage ends (either because you retire or leave the job), you get a Special Enrollment Period of eight months to sign up for Part B without any penalty. Miss that eight-month window, and the standard late enrollment penalties kick in.
COBRA Does Not Count
This is where many people get tripped up. COBRA continuation coverage does not protect you from Part B penalties. Your eight-month Special Enrollment Period starts when you stop working or lose your employer health insurance, whichever comes first. Choosing COBRA doesn’t extend that clock. If you rely on COBRA instead of enrolling in Medicare and the eight months pass, you’ll face the same lifetime penalties and the same enrollment waiting periods as anyone else who missed the deadline.
Once you do enroll in Medicare, your COBRA coverage will probably end automatically.
Part A Is Usually Penalty-Free
Most people get Part A (hospital coverage) premium-free because they or a spouse paid Medicare taxes for at least 10 years. If you qualify for premium-free Part A, there’s no penalty for signing up late, though delaying still means you won’t have hospital coverage in the meantime.
The small number of people who don’t qualify for premium-free Part A do face a late enrollment penalty: their Part A premium goes up by 10% for twice the number of years they could have been enrolled but weren’t. Unlike the Part B penalty, this one eventually expires.
The HSA Tax Trap
If you’re still working past 65 and contributing to a Health Savings Account, Medicare enrollment creates a tax complication you need to plan for. When you enroll in Medicare Part A after age 65, your coverage is applied retroactively for up to six months (though not before the month you turned 65). During any month you’re considered covered by Medicare, you’re not eligible to contribute to an HSA.
This means if you’ve been contributing to your HSA during those retroactive months, the IRS treats those contributions as excess. You’ll either need to withdraw the overcontributions before filing your taxes for that year or file an amended return. Failing to do so results in a tax penalty on the excess amount.
The practical takeaway: if you plan to delay Medicare because you’re still working and want to keep funding your HSA, you should stop contributing at least six months before you eventually enroll. That way, the retroactive coverage period won’t overlap with any contributions.
How the Penalties Add Up Over Time
The financial impact of late enrollment compounds because the penalties are percentage-based and permanent. As Medicare premiums rise each year (which they consistently do), your penalty amount rises proportionally. Someone paying a 20% Part B surcharge in their late 60s will be paying that same 20% on a much higher base premium in their 80s.
For someone who delayed both Part B and Part D by three years without qualifying coverage, the combined extra cost could easily exceed $100 per month. Over a 20-year span of Medicare enrollment, that’s more than $24,000 in avoidable penalties, and likely more as premiums increase.
The system is designed to encourage enrollment when you’re first eligible. If you have employer coverage that qualifies, you’re protected. If you don’t, the cost of waiting only grows.