If you’re collecting Social Security retirement benefits, Medicare Part A is effectively mandatory once you turn 65, but Medicare Part B is not. Federal law automatically entitles Social Security recipients to premium-free Part A hospital insurance, and there is no way to opt out while keeping your retirement checks. Part B, which covers doctor visits and outpatient care, carries a monthly premium and can be declined, though skipping it without other qualifying coverage triggers a lifetime late enrollment penalty.
What Happens Automatically at 65
If you’re already receiving Social Security retirement benefits at least four months before your 65th birthday, the Social Security Administration enrolls you in both Part A and Part B without any application on your end.1Medicare.gov. I’m Getting Social Security Benefits Before 65 A welcome package with your Medicare card arrives about three months before you turn 65, and coverage begins the first day of your birthday month. One quirk: if your birthday falls on the first of the month, coverage starts the first day of the prior month.2Centers for Medicare & Medicaid Services. Original Medicare (Part A and B) Eligibility and Enrollment
The package gives you a choice on Part B, not on Part A. Whether you do anything or nothing, Part A is yours.
Why You Cannot Drop Part A
Once you’re 65 and drawing Social Security, you are legally entitled to premium-free Part A, and that entitlement is not optional. In Hall v. Sebelius (2012), the D.C. Circuit rejected an attempt by a group of retirees to disclaim their Part A entitlement while continuing to receive Social Security. The court held that no statutory mechanism exists to do so.3Justia Law. Hall, et al. v. Sebelius, et al., No. 11-5076 (D.C. Cir. 2012)
The court did draw one distinction worth understanding. You can always decline to use Part A for any specific hospital stay and pay out of pocket or bill private insurance instead. What you cannot obtain is a legal declaration that you are not entitled to Part A. The entitlement follows automatically from collecting Social Security at 65.
There is one exit, and for most people it’s theoretical. You can terminate Part A by withdrawing from Social Security entirely, which requires repaying every dollar of retirement income you have already received, plus any Part A benefits Medicare has paid on your behalf.4Medicare. How to Drop Part A and Part B After a few years of checks, the number is usually too large to consider.
How to Decline Part B
Part B is different because it carries a monthly premium, so the government treats it as voluntary. If you don’t want it, the back of your Medicare card includes instructions for refusing coverage. You check the box declining medical insurance, sign the card, and return it to the Social Security Administration. The agency then issues a replacement card showing only Part A.4Medicare. How to Drop Part A and Part B Keep a photocopy of the signed card. If there’s ever a dispute about when you declined, that documentation matters.
The Cost of Declining Part B
Declining Part B is rarely a good idea unless you have qualifying employer coverage, because the late enrollment penalty is permanent. For every full 12-month period you could have had Part B but didn’t enroll, your future premium goes up by 10%, and that surcharge sticks for as long as you have Part B.5Medicare.gov. Avoid Late Enrollment Penalties
The math compounds quickly. On the 2026 standard premium of $202.90, a two-year delay adds roughly $40 a month, or about $487 a year, for the rest of your life. A five-year delay pushes the surcharge past $1,200 annually. There is no forgiveness window and no cap on how long the penalty runs.
Part D prescription drug coverage carries its own separate penalty. Go 63 or more consecutive days without creditable drug coverage after becoming eligible, and you’ll owe 1% of the national base beneficiary premium for each uncovered month, added to your Part D premium for as long as you carry it.5Medicare.gov. Avoid Late Enrollment Penalties
When Declining Part B Makes Sense
The one situation where skipping Part B is genuinely safe is active employer coverage, and the rules depend on the size of the employer.
If the employer has 20 or more employees, the group plan pays first and Medicare is secondary. You can delay Part B without any penalty as long as you or your spouse remain actively employed and covered.6Social Security Administration. Sign Up for Part B Only Part A keeps running in the background as secondary insurance for hospital stays.
If the employer has fewer than 20 employees, the order flips. Medicare becomes primary and the employer plan pays second, which usually means enrolling in Part B is a practical necessity even though you technically have job-based insurance.7Social Security Administration. How to Apply for Medicare Part B During Your Special Enrollment Period
One trap catches people every year: COBRA is not active employer coverage for these purposes. If you’re on COBRA when you turn 65, delaying Part B does not qualify you for a Special Enrollment Period later, and the late penalty will start accumulating.
Signing Up After Employer Coverage Ends
When active employer coverage ends, you have an 8-month Special Enrollment Period to sign up for Part B without penalty. You’ll file form CMS-40B along with form CMS-L564, which is the employer’s confirmation that you had qualifying coverage.6Social Security Administration. Sign Up for Part B Only Miss the 8-month window and your only fallback is the General Enrollment Period from January 1 through March 31, with coverage starting the month after you sign up.8Medicare. When Does Medicare Coverage Start That’s how people end up uninsured for months and paying a permanent penalty on top of it.
Your employer should send an annual notice stating whether its prescription drug plan is “creditable,” meaning at least as good as standard Part D.9Centers for Medicare & Medicaid Services. Model Notice Letters Save that notice. It’s your proof if the SSA later questions why you delayed Part D.
The HSA Trap Nobody Warns You About
If you contribute to a Health Savings Account, mandatory Part A enrollment creates a tax problem. Once you’re enrolled in any part of Medicare, including Part A alone, you can no longer make HSA contributions. Your contribution limit drops to zero starting the first month of Medicare coverage.10Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Accounts
It gets worse because Part A can be backdated. When you apply for Medicare after age 65, Part A coverage is retroactive up to six months, though not before the month you turned 65. Any HSA contributions you made during those retroactive months become excess contributions, subject to a 6% excise tax each year they stay in the account.10Internal Revenue Service. Publication 969 (2025), Health Savings Accounts and Other Tax-Favored Accounts
The workaround is simple but needs planning. Stop HSA contributions at least six months before you enroll in Medicare. If you’re collecting Social Security and will be auto-enrolled at 65, that means halting contributions six months before your 65th birthday. You can still spend down the existing balance on qualified medical expenses after enrolling; the restriction hits new contributions only.
If You’re on Social Security Disability
Disability recipients follow the same framework with a different clock. After 24 consecutive months of SSDI benefits, you’re automatically enrolled in Medicare.11Social Security Administration. Medicare Information From that point forward, Part A is mandatory as long as you continue to receive disability benefits, Part B is voluntary, and the same late enrollment penalties apply if you decline Part B without qualifying alternative coverage.1Medicare.gov. I’m Getting Social Security Benefits Before 65