When to Sign Up for Medicare — and What a Late Penalty Costs

1The deadline: a seven-month window around your birthday

Your initial enrollment period starts three months before the month you turn 65, includes your birthday month, and ends three months after it. No one sends a reminder when it opens, unless you are already receiving Social Security or Railroad Retirement benefits, in which case you are enrolled in Parts A and B automatically and your card arrives about three months before your birthday.

When you sign up within the window decides when coverage begins. For someone who turns 65 on July 15, 2026, it looks like this:

The practical lesson: if you need Medicare from your birthday month, sign up in the three months before it. Waiting until the last month of the window does not cost a penalty, but it does leave a gap.

2Why this one date carries so much weight

Medicare's late penalties exist to discourage people from waiting until they are sick to enroll. The effect, for anyone who simply misses the window, is that a single oversight becomes a permanent cost. Signing up when you did not need to can cost money too, for example if you are still contributing to a health savings account. So the decision deserves a little attention a few months before your birthday, not in the week after.

3The big exception: you or your spouse still work

If you or your spouse are actively working and covered by that employer's group health plan, you can usually delay Part B without a penalty. When the job or the coverage ends, whichever comes first, a special enrollment period gives you eight months to sign up, starting the month after.

The size of the employer matters. If it has 20 or more employees, its plan pays first and delaying Part B is normally safe. If it has fewer than 20, Medicare is supposed to pay first once you are eligible, and the employer plan may pay little for care Part B would have covered. In that case you generally need Part B at 65. Ask the plan in writing before you decide.

Retiree coverage and COBRA do not count. Coverage from a former employer, including retiree benefits and COBRA continuation, is not coverage from current work. It does not protect you from the penalty, and the eight-month clock starts when you stop working, not when COBRA ends. This is one of the most common ways people end up paying a penalty they never saw coming.

Health savings accounts need a head start. Once you have any part of Medicare, including premium-free Part A, you can no longer contribute to an HSA. Part A is backdated up to six months when you sign up after 65, so stop contributions at least six months before you apply.

4What happens if you miss it

If your initial window has closed and you have no special enrollment period, you can sign up only during the general enrollment period, January 1 to March 31, with coverage starting the month after you sign up. Someone who realizes in April that they missed their window waits until January to apply, and has no Part B in between.

Then come the penalties, and they work differently for Part B and Part D.

Swipe sideways to see the whole table.

Partial years do not count toward the Part B penalty: 11 months late costs nothing extra, 13 months late costs 10 percent. The Part D penalty is triggered by going 63 days or more in a row without creditable drug coverage after your window ends, and it follows you from plan to plan.

5Who else gets a second chance

Since 2023, Medicare allows special enrollment periods for some exceptional situations: losing Medicaid coverage, being released from incarceration, a natural disaster that kept you from enrolling, or being given wrong information by an employer or health plan. Contact Social Security to ask whether your situation qualifies.

• People on disability: after 24 months of Social Security disability benefits you are enrolled automatically, whatever your age.
• People with a Medicare Savings Program: if the program pays your premium, the Part B penalty is generally not charged; see Medicare Savings Programs and Extra Help.
• Marketplace enrollees: a Marketplace plan does not let you delay Part B without a penalty, and any premium tax credit ends once you can get premium-free Part A.
• Veterans and military retirees: VA health care does not protect you from the Part B penalty, though VA drug coverage counts as creditable for Part D. TRICARE For Life requires Part B.

6Working back from your birthday

A simple timeline keeps the deadlines from sneaking up. Counting back from the month you turn 65:

1. Six months before: if you contribute to a health savings account and plan to take Part A later, decide when to stop contributions.
2. Four to five months before: if you or your spouse have employer coverage, ask the plan in writing whether it pays first or second once you are eligible, and whether its drug coverage is creditable.
3. Three months before: your window opens. Sign up for Part A and, unless you are delaying it under the employer rules, Part B.
4. Before your birthday month: choose drug coverage, either a Part D plan or a Medicare Advantage plan that includes it, and compare Medigap policies if you are staying with Original Medicare.
5. After coverage starts: check that your premium is being taken from your Social Security payment or billed correctly, and keep your Medicare card with your insurance papers.

7How to sign up, and what comes next

You sign up for Parts A and B through Social Security: online at ssa.gov, by phone or at a local office. If you are using the eight-month window after employer coverage ends, you also send a form your employer completes confirming when you had coverage from current work.

Drug coverage is a separate decision. You choose a Part D plan, or a Medicare Advantage plan that includes drugs, from private insurers during your initial window; our guide to Original Medicare and Medicare Advantage compares the two routes, and our Part D guide explains drug coverage. If you choose Original Medicare, the six months starting when you are 65 and enrolled in Part B are the best time to buy a Medigap supplement, because insurers cannot refuse you or charge more for your health.

After that, the calendar gets kinder. Each year from October 15 to December 7 you can change drug and Medicare Advantage plans, with the change taking effect January 1. For how Medicare fits with other coverage, see Medicare and Medicaid.