When You Must Enroll in Medicare While Receiving SSDI

Medicare enrollment is mandatory once you've been on SSDI for 24 months, but the timing and consequences of missing that window vary by your situation

If you receive Social Security Disability Insurance (SSDI), you do not have a choice about Medicare after a certain point. The Social Security Administration automatically enrolls you in Medicare Part A (hospital insurance) and Part B (medical insurance) once you have been receiving SSDI benefits for 24 consecutive months. This is not optional, and the enrollment happens whether you want it or not.

The 24-month clock starts from the month you first became may have access to to SSDI benefits—not from the month you applied, and not from the month your first check arrived. If you were approved retroactively (meaning Social Security determined your disability began months or years before you applied), the 24 months count backward from that established onset date. This matters because some people discover they are already Medicare-enrolled when they receive their first SSDI payment.

You can decline Part B coverage before it takes effect, but declining Part A is not an option. Part A has no monthly premium for most SSDI beneficiaries, so the government does not allow you to refuse it. Part B, which costs a monthly premium, can be turned down—but if you do and later change your mind, you may face a permanent penalty on your premium.

Key Takeaways

Medicare Part A enrollment is automatic and mandatory after 24 months on SSDI; you cannot refuse it, and it has no monthly premium for most beneficiaries.
Medicare Part B enrollment is also automatic after 24 months, but you can decline it in writing before coverage begins without penalty.
If you decline Part B and later enroll, your monthly premium will be permanently higher unless you have a may have access to life event.
The 24-month period is counted from your SSDI entitlement date, not your process date, and includes any retroactive months Social Security awards you.
You receive a Medicare card in the mail about three months before your automatic enrollment takes effect, giving you time to decline Part B if you choose.

How the 24-month countdown works

Social Security tracks your entitlement date separately from your process date. Your entitlement date is the first month you met the disability criteria according to Social Security's decision—which may be months before you filed your claim. When you receive a disability approval letter, it states both your process date and your entitlement date. The 24-month Medicare countdown begins on your entitlement date.

Example: You explore for SSDI in March 2024, but Social Security determines your disability began in September 2023. Your entitlement date is September 2023. Your 24-month countdown starts then. In September 2025, you become Medicare-may be able to access, even though you have only been receiving monthly payments for 18 months.

If you are unsure of your entitlement date, check your Social Security award letter or call Social Security at 1-800-772-1213. You can also view your entitlement date in your my Social Security account online. Knowing this date lets you plan ahead for when Medicare will begin.

What happens when you turn 65

If you reach age 65 while still on SSDI, your SSDI benefits automatically convert to Social Security retirement benefits at the same payment amount. Your Medicare coverage does not change—you keep the same Part A and Part B enrollment. The conversion is administrative only; your monthly check stays the same, and your healthcare coverage continues without interruption.

This conversion matters mainly for record-keeping and for understanding which program you are technically receiving from. For Medicare purposes, it makes no difference whether you are on SSDI or retirement benefits. Your coverage, premiums, and out-of-pocket costs remain identical.

Declining Part B before it starts

You can refuse Medicare Part B coverage, but you must do so before your coverage begins. Social Security sends you a Medicare card and an enrollment notice about three months before your automatic enrollment takes effect. The notice explains your options and how to decline Part B if you wish.

To decline Part B, you must return a signed form to Social Security or submit a written request stating that you do not want Part B coverage. Verbal requests over the phone are not sufficient; Social Security requires a written record. If you miss the important date and Part B coverage begins, you can still drop it, but you will face a permanent premium increase if you later re-enroll.

Declining Part B makes sense only if you have other health insurance—such as employer coverage or a spouse's plan—that is as good as or better than Medicare Part B. If you have no other coverage, declining Part B usually costs you more in the long run because the penalty is permanent.

The Part B late enrollment penalty

If you decline Part B when it is first offered and later change your mind, your monthly Part B premium will be permanently higher. The penalty is 10 percent of the standard Part B premium for each full 12 months you were may be able to access but not enrolled. This penalty stays with you for life, even if you switch to a different Medicare plan.

Example: The standard Part B premium in 2024 is $164.90 per month. If you decline Part B at age 26 (when you become Medicare-may be able to access after 24 months on SSDI) and enroll at age 30, you owe a penalty of 40 percent (four years × 10 percent per year). Your Part B premium would be roughly $231 per month instead of $164.90, and that higher amount applies for the rest of your life.

The only way to avoid this penalty is to have a may have access to life event—such as losing employer coverage or gaining a spouse with employer coverage—that allows you to enroll without penalty during a special enrollment period. Otherwise, the penalty is permanent.

Medicare and other health insurance you may have

If you are covered under a parent's health insurance plan (because you are under age 26) or under an employer's plan, Medicare becomes your secondary insurance once you are automatically enrolled. This means your other insurance pays first, and Medicare pays second. You keep both coverages, and you do not lose your other insurance because Medicare begins.

If you are on Medicaid (state health insurance for low-income people), Medicare and Medicaid work together. Medicare is primary, and Medicaid covers some costs that Medicare does not, such as copayments and deductibles. You can be on both programs at the same time. Medicaid does not end when Medicare begins.

If you have employer coverage through your own job or a family member's job, you can keep that coverage even after Medicare starts. Coordinate with your employer's benefits department to understand how your coverage will work once Medicare is primary.

What to do when you receive your Medicare card

When Social Security sends you your Medicare card, review it carefully for errors. Check that your name, date of birth, and Social Security number are correct. If anything is wrong, contact Medicare at 1-800-MEDICARE (1-800-633-4227) to request a corrected card.

Your Medicare card will show whether you have Part A only or both Part A and Part B. If you want to decline Part B, the enrollment notice that comes with your card will explain the important date and how to submit your decline. Do this in writing and keep a copy for your records.

Once your Medicare coverage begins, you can use your Medicare card at any hospital, doctor's office, or pharmacy that accepts Medicare. You do not need to do anything else to set up your coverage—it begins automatically on the first day of the month after your 24-month SSDI period ends.

Frequently Asked Questions

Can I delay Medicare enrollment if I don't want it yet?

No. Part A enrollment is automatic and cannot be delayed or refused. Part B enrollment is also automatic, but you can decline it in writing before coverage begins. If you decline Part B, you can enroll later during the general enrollment period (January through March each year), but you will owe a permanent premium penalty.

What if I'm still working and have employer health insurance?

You keep both. Your employer insurance remains primary, and Medicare becomes secondary. You do not lose your employer coverage because Medicare begins. Coordinate with your employer's benefits department to understand how the two plans work together.

Does Medicare cost money if I'm on SSDI?

Part A has no monthly premium for most SSDI beneficiaries. Part B has a monthly premium (the standard amount in 2024 is $164.90, though it varies by income). The premium is deducted from your SSDI check automatically once Part B begins.

What if I miss the important date to decline Part B?

If Part B coverage begins and you did not decline it, you can still drop it later. However, if you re-enroll in Part B in the future, you will owe a permanent 10 percent premium penalty for each year you were may be able to access but not enrolled. The only exception is if you have a may have access to life event that allows a special enrollment period.

How do I know when my 24 months will be up?

Check your SSDI award letter for your entitlement date, then count forward 24 months. You can also call Social Security at 1-800-772-1213 or log into your my Social Security account to confirm the date. Social Security will send you a Medicare enrollment notice about three months before coverage begins.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.