Say your 65th birthday lands in September. Your window to sign up for Medicare opened June 1 and closes December 31. That seven-month stretch, three months before your birthday month, the month itself, and three months after, is your Initial Enrollment Period, and what you do with it can follow you for the rest of your life.

Medicare enrollment is one of those money decisions where the deadline does most of the deciding. Sign up on time and the process is boring, which is exactly what you want. Miss it without qualifying coverage and you can face premium penalties that never go away plus months without insurance. Here is the timeline, the traps, and the one big exception for people still working.

The seven-month window, month by month

Your Initial Enrollment Period is built around the month you turn 65. Sign up during the three months before your birthday month, and your coverage starts the first day of your birthday month. Sign up during your birthday month or the three months after, and coverage starts the first of the month after you enroll.

That second sentence is worth reading twice, because it changed a few years ago in retirees’ favor. It used to be that late-window signups waited two or three months for coverage. Now it is simply the next month. Still, the practical advice is unchanged: enroll in the early months of your window so coverage begins the moment you are eligible, with no gap.

One quirk: if your birthday falls on the first of the month, the whole schedule shifts a month earlier, as if your birthday were in the prior month.

What you’re signing up for (and what it costs in 2026)

Original Medicare comes in two parts. Part A covers hospital stays and is premium-free for most people, because you or a spouse paid Medicare taxes for at least 10 years of work. Part B covers doctor visits and outpatient care, and it carries a monthly premium: the standard rate is $202.90 in 2026, with a $283 annual deductible, per the official CMS figures. Higher-income households pay more.

Enrollment itself runs through Social Security. If you are already collecting Social Security benefits, you will be enrolled in Parts A and B automatically around your 65th birthday. If you are not collecting yet, and more people are waiting these days, nothing happens automatically. You apply online at ssa.gov/medicare, which takes most people well under an hour.

The late penalty math nobody should learn firsthand

Here is why the window matters so much. If you skip Part B when you are first eligible and do not have other qualifying coverage, your monthly premium goes up 10 percent for each full 12-month period you could have had Part B but didn’t. And that surcharge is not a slap on the wrist that expires; you pay it for as long as you have Part B, which generally means for life.

Run the numbers at 2026 rates. Two years late means a 20 percent penalty, about $40.58 added to every monthly premium, roughly $487 a year, every year, forever, and the dollar amount grows each time premiums rise. Part D drug coverage has its own separate late penalty that accrues month by month without creditable drug coverage, and premium-free Part A has no penalty for most people, though those who must buy Part A face a temporary surcharge if late.

On top of the penalty, enrolling late usually means waiting for the General Enrollment Period, January 1 through March 31 each year, to sign up at all. That can leave you facing months with no coverage.

Still working at 65? The rules are different

Here is the big exception. If you (or your spouse) are still working at 65 and you have health coverage through that current employer, you generally do not need to enroll in Part B yet and will not face a penalty for waiting. When the job or the coverage ends, you get a Special Enrollment Period, eight months to sign up penalty-free.

Two traps hide inside this exception. First, the employer coverage must come from current employment. COBRA and retiree health plans do not count; if that is what you have at 65, sign up for Medicare on time. Second, at smaller employers (fewer than 20 employees), Medicare generally becomes the primary payer at 65, so skipping enrollment can leave you effectively uninsured even while premiums are being deducted for the workplace plan. If you work for a small company, talk to the benefits administrator before your window opens.

Many working folks split the difference: they take premium-free Part A at 65 and delay Part B until retirement. One caution there: you cannot contribute to a Health Savings Account once any part of Medicare is in effect, so HSA savers often delay Part A too.

A simple plan for your 64th year

Three or four months before your 65th birthday, do three things. Confirm how your current coverage interacts with Medicare, especially if you are still working. Create your my Social Security account if you do not have one, so enrollment is a matter of clicks rather than phone queues. And decide your path: Original Medicare (usually with a Part D drug plan and possibly a Medigap policy) or a Medicare Advantage plan. Free, unbiased help is available from your State Health Insurance Assistance Program, and the plan-comparison tools at medicare.gov are genuinely useful. The window is seven months, but the people who have the easiest time treat it like it is seven weeks.

This article was produced with AI assistance and reviewed by a human editor. Figures are linked to their primary sources; where a claim could not be verified from the public record, we say so.