No, signing up for Medicare at age 65 is not legally mandatory. You won’t face fines or legal consequences for skipping it. But in most situations, delaying enrollment triggers permanent financial penalties that make your premiums more expensive for the rest of your life. Whether you should sign up at 65 depends almost entirely on whether you have qualifying health coverage through a current employer.
What Happens Automatically at 65
If you’re already receiving Social Security benefits when you turn 65, you don’t need to do anything. You’ll be automatically enrolled in both Part A (hospital coverage) and Part B (outpatient and doctor coverage). Your Part B premium, $202.90 per month in 2026, will be deducted from your Social Security check unless you actively opt out.
If you’re not yet collecting Social Security, you need to sign up yourself. Your window is a seven-month stretch called the Initial Enrollment Period: it starts three months before the month you turn 65 and ends three months after. Missing this window is where the penalties start.
Who Can Safely Delay Without Penalties
The major exception is people who are still working and covered by an employer health plan. If your employer (or your spouse’s employer) has 20 or more employees and provides group health insurance, that plan pays first and Medicare pays second. In this situation, you can delay Part B enrollment without any penalty. Once you leave the job or lose that coverage, you get a Special Enrollment Period to sign up.
The 20-employee threshold matters a lot. If your employer has fewer than 20 workers, Medicare becomes the primary payer even while you’re still working. That means delaying Part B with a small employer’s plan could leave you with significant gaps in coverage and trigger the late penalty on top of it. Multi-employer plans follow slightly different rules: if any participating employer in the plan has 20 or more employees, the large-employer rules generally apply to everyone in the plan.
COBRA coverage does not count as employer coverage for this purpose. If you’re on COBRA when you turn 65, you still need to enroll during your Initial Enrollment Period.
The Part B Late Enrollment Penalty
If you miss your enrollment window and don’t have qualifying employer coverage, your Part B premium increases by 10% for every full 12-month period you could have signed up but didn’t. So if you waited three years past your deadline, you’d pay 30% more than the standard premium. This surcharge is permanent. It stays on your premium for as long as you have Part B, which for most people means the rest of their life.
At the 2026 standard premium of $202.90, a 30% penalty adds roughly $61 per month. That’s over $700 a year in extra costs, every year, indefinitely.
Part A: Usually Free, Usually Worth Taking
Part A is premium-free for most people. You qualify at no cost if you or your spouse earned enough work credits through Social Security taxes, typically about 10 years of work. Since it costs nothing, there’s rarely a reason to delay it, even if you have employer coverage.
One important exception: if you have a Health Savings Account. Once you enroll in any part of Medicare, including Part A, you can no longer contribute to an HSA. If you want to keep funding your HSA past 65, you may choose to delay Part A. Just be aware that when you do eventually apply for Social Security, Part A enrollment is retroactive up to six months. You and your employer should stop HSA contributions six months before you apply for Social Security or retire to avoid a tax penalty.
People who don’t qualify for premium-free Part A can purchase it, but only during designated enrollment periods. There’s a late penalty for Part A as well, though it applies to a much smaller group of people.
The Part D Penalty Works Differently
Part D covers prescription drugs. You don’t have to enroll in a Part D plan at 65, but if you go without “creditable” drug coverage (coverage that’s at least as good as a standard Medicare drug plan) for 63 or more consecutive days, you’ll owe a penalty when you do eventually sign up. The surcharge is 1% of the national average drug plan premium for every full month you were uncovered. Like the Part B penalty, this one is recalculated each year and lasts as long as you have Part D coverage.
Special Cases: TRICARE and Veterans
If you’re a military retiree planning to use TRICARE for Life after 65, enrollment in both Part A and Part B is required. TRICARE for Life acts as a supplement that covers costs Medicare doesn’t, but it only works if you’re enrolled in both parts. Skip Part B, and you lose TRICARE for Life eligibility entirely.
Veterans who get care through the VA have a different situation. VA benefits are not considered employer coverage, but they do count as creditable coverage for Part D purposes. You won’t face a drug plan penalty as long as you maintain VA prescription benefits. However, VA coverage doesn’t protect you from the Part B penalty. If you want the flexibility to see doctors outside the VA system, delaying Part B past 65 without qualifying employer coverage will cost you.
What Happens If You Miss the Window
If you didn’t sign up during your Initial Enrollment Period and don’t qualify for a Special Enrollment Period through employer coverage, you’ll have to wait for the General Enrollment Period, which runs January 1 through March 31 each year. Coverage won’t start until July 1 of that year. During the gap, you’d be uninsured or relying on whatever non-Medicare coverage you can find, and the late penalty will apply once coverage begins.
Several life events open Special Enrollment Periods outside the normal schedule. Losing employer or union coverage gives you two full months after your coverage ends to enroll in a Medicare Advantage or drug plan. Moving out of your plan’s service area, leaving a nursing facility, or losing Medicaid eligibility also trigger enrollment windows ranging from two to three months.
The Bottom Line on Timing
Medicare enrollment at 65 is technically voluntary, but the system is designed to make delay costly for anyone who doesn’t have active employer coverage from a company with 20 or more employees. Part A is free for most people and worth enrolling in immediately unless you’re actively contributing to an HSA. Part B and Part D carry permanent penalties that compound with every year you wait. For the majority of people turning 65, signing up on time isn’t legally required, but it’s financially irrational not to.