Guide

The Initial Enrollment Period, explained

Figures and rules on this page last checked against their sources: October 25, 2026.

Your first chance to sign up for Medicare Parts A and B is a seven-month window around your 65th birthday, called the Initial Enrollment Period. Sign up inside it and no late penalty applies. Sign up early in it and your coverage starts the month you turn 65.

To see your own seven months, use the sign-up window tool. This page explains how the window works and what to decide while it is open.

How the seven months are counted

The window starts three months before the month you turn 65. It includes that month. It ends three months after it.¹

So if you turn 65 in August 2027, your window runs from May 1, 2027 to November 30, 2027.

The window opens whether you are still working, already retired or getting Social Security. What changes from person to person is whether you need to act in it, which the rest of this page covers.

If your birthday is on the 1st of the month

Social Security counts you as reaching an age on the day before your birthday.² If you were born on the 1st, that day falls in the previous month. So your whole window moves one month earlier. It starts four months before your birthday month and ends two months after it.³

Medicare.gov gives this example: a birthday on June 1 means a window of February through August. Sign up in February, March or April, and coverage starts May 1.³

A January 1 birthday works the same way. For Medicare, you turn 65 in December of the year before.

When your coverage starts

Coverage always starts on the first day of a month. Which month depends on when you sign up:⁴

In the first three months of the window: Part B starts on the first day of the month you turn 65.
In the month you turn 65, or any of the three months after: Part B starts on the first day of the month after you sign up.

This rule covers everyone who turned 65 in January 2023 or later, counting a birthday on the 1st as described above. For people who turned 65 before then, an older rule applied: signing up in the last three months of the window started Part B two or three months after the month you signed up.⁴ Articles written before 2023 may still describe those delays, so check the date on anything you read.

Premium-free Part A works a little differently. If you qualify for it, Part A starts the month you turn 65. If you sign up for Part A later, its start reaches back up to six months, though never to before the month you turned 65.⁵

Signed up for you, or sign up yourself

If you already get Social Security or Railroad Retirement benefits at least four months before you turn 65, you are signed up for Parts A and B automatically. Because Part B has a monthly premium, you can choose whether to keep it.⁶

Everyone else signs up through Social Security: online at ssa.gov/medicare/sign-up, or by phone at 1-800-772-1213; TTY 1-800-325-0778⁷. If you or your spouse worked for a railroad, call the Railroad Retirement Board at 1-877-772-5772⁸.

What it costs in 2026

Most people pay no premium for Part A, because they or a spouse paid Medicare taxes while working, usually for 10 years.⁹

Part B has a standard premium of $202.90 a month¹⁰ in 2026 and a yearly deductible of $283¹¹. People with higher incomes pay more. In 2026 the extra charge starts above $109,000 for a single return, $218,000 for a joint return¹² of modified adjusted gross income, as shown on your tax return from two years before: 2024's return for the 2026 premium.¹³

The 2027 Part B premium had not been announced when this page was last checked.¹⁴ The page on what changed for 2027 is updated when it is.

If you have job-based coverage at 65

The window still opens, but you may not need Part B during it. If you or your spouse are still working and covered by that employer's plan, you can usually sign up later without a penalty, using a Special Enrollment Period.¹⁵

Whether waiting makes sense depends partly on the size of the employer. With 20 or more employees, the job plan generally pays first. With fewer than 20, Medicare pays first, and the job plan might not pay if you don't have both parts.¹⁶ The details are in Still working at 65.

If you miss it

If you don't sign up in your window and don't qualify for a Special Enrollment Period, your next chance is the General Enrollment Period, January 1 to March 31 each year. Coverage then starts the month after you sign up.¹⁷

A late penalty may also apply: 10% added to your Part B premium for each full 12 months you could have had Part B but didn't, usually for as long as you have Part B.¹⁸ The penalty estimate works out the figure for your dates.

Two other clocks start at the same time

Drug coverage. If you go 63 days or more without drug coverage at least as good as Medicare's (called creditable coverage), a Part D penalty can apply. It is 1% of a national base premium for each month, added for as long as you have Medicare drug coverage.¹⁹

Medigap. If you choose Original Medicare and want a Medicare Supplement (Medigap) policy, your best time to buy is the six months that start when you are 65 and have Part B. During those months you can buy any policy sold in your state, even with health problems. Afterwards, under federal rules, insurers generally don't have to sell you one.²⁰ Some states give more rights; your State Health Insurance Assistance Program can tell you yours.²¹

A short checklist

Find your seven months with the window tool and write them on your calendar.
Work out whether you will be signed up automatically. If you don't get Social Security yet, plan to sign up yourself.
If you have job coverage, ask the benefits office how its plan works with Medicare and how many employees it counts.
If you put money into a health savings account, settle that first. You can't contribute once you have Medicare, and Part A can reach back up to six months, so Medicare.gov suggests stopping contributions at least six months before you apply.²²
To have coverage from the month you turn 65, sign up in the first three months of the window.
Keep copies of what you send and the letters you receive.

For one-on-one help, every state has a free State Health Insurance Assistance Program.²³ Medicare's own line is 1-800-MEDICARE (1-800-633-4227); TTY 1-877-486-2048²⁴.

More guides

Still working at 65: job coverage and the Special Enrollment PeriodIf you or your spouse have health coverage from a current job at 65, you can often put off Part B without a penalty. How the 8-month Special Enrollment Period works, and where people get caught.

The Part B late-enrollment penalty, and how to avoid itMiss your sign-up window and Part B can cost 10% more for each full year you waited, for as long as you have it. How the months are counted, with worked examples.

An Open Enrollment checklist, October 15 to December 7What you can change during Medicare's fall Open Enrollment, what you can't, and a step-by-step list for reviewing your plan before December 7.

Your plan is leaving: what to do when a Medicare Advantage plan endsIf your Medicare Advantage plan won't be offered next year, you have a special right to choose another plan, a right to buy a Medigap policy, and dates that matter. What happens if you do nothing.

Sources for this page

Initial Enrollment Period: seven months around the month you turn 65. Source: Electronic Code of Federal Regulations, 42 CFR 407.14: Initial enrollment period; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Social Security counts you as reaching an age the day before your birthday. Source: Electronic Code of Federal Regulations, 20 CFR 404.2(c)(4): Attainment of age. Checked October 25, 2026.

Birthday on the 1st: the window starts and ends a month earlier. Source: Medicare.gov, When does Medicare coverage start?; Electronic Code of Federal Regulations, 20 CFR 404.2(c)(4): Attainment of age. Checked October 25, 2026.

When Part B starts, by the month you sign up: for people who turned 65 from January 2023, the first 3 months of the window give the month you turn 65 and the last 4 the month after you sign up; before January 2023, the last 3 months gave 2 or 3 months after you sign up. Source: Electronic Code of Federal Regulations, 42 CFR 407.25: Beginning of entitlement; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Premium-free Part A starts the month you turn 65; signing up later, it reaches back up to 6 months (not before 65). Source: Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Getting Social Security at least 4 months before 65 signs you up for Parts A and B automatically. Source: Medicare.gov, How do I sign up for Medicare?. Checked October 25, 2026.

Social Security's phone line. Source: Medicare.gov, How do I sign up for Medicare?. Checked October 25, 2026.

The Railroad Retirement Board's phone line, for people who worked for a railroad. Source: Medicare.gov, How do I sign up for Medicare?. Checked October 25, 2026.

Most people pay no Part A premium: usually 10 years of work, yours or a spouse's. Source: Medicare.gov, Avoid late enrollment penalties. Checked October 25, 2026.

Part B standard monthly premium. $202.90 a month (2026). Source: Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet), November 14, 2025. Checked October 25, 2026.

Part B yearly deductible. $283 (2026). Source: Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet), November 14, 2025. Checked October 25, 2026.

Income above which Part B costs more (2026). $109,000 for a single return, $218,000 for a joint return (2026). Source: Centers for Medicare & Medicaid Services, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet), November 14, 2025. Checked October 25, 2026.

The higher Part B premium is based on income on your tax return from two years before (2024 for 2026). Source: Medicare.gov, Medicare costs. Checked October 25, 2026.

Part B standard monthly premium. not yet announced. Source: Centers for Medicare & Medicaid Services, CMS Newsroom. Checked October 25, 2026.

Special Enrollment Period for job-based coverage: any time while covered, or 8 months after the job or the coverage ends, whichever is first. Source: Medicare.gov, When does Medicare coverage start?; Medicare.gov, When can I sign up for Medicare?. Checked October 25, 2026.

Employer with 20 or more employees: the job plan pays first; fewer than 20: Medicare pays first. Source: Medicare.gov, Who pays first?; Medicare.gov, When can I sign up for Medicare?. Checked October 25, 2026.

General Enrollment Period: January 1 to March 31; coverage starts the month after you sign up. Source: Electronic Code of Federal Regulations, 42 CFR 407.15: General enrollment period; Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Part B late-enrollment penalty: 10% for each full 12 months, usually for as long as you have Part B. Source: Medicare.gov, Avoid late enrollment penalties; Electronic Code of Federal Regulations, 42 CFR 408.22: Increased premiums for late enrollment. Checked October 25, 2026.

Part D penalty: 1% of the base premium for each month without creditable drug coverage (63 days or more). Source: Medicare.gov, Avoid late enrollment penalties. Checked October 25, 2026.

Medigap Open Enrollment: 6 months from when you are 65 and have Part B. Source: Medicare.gov, Buying a Medigap policy; Medicare.gov, When can I buy a Medigap policy?. Checked October 25, 2026.

These Medigap rights are federal; your state may give you more. Source: Medicare.gov, When can I buy a Medigap policy?. Checked October 25, 2026.

No HSA contributions once you have Medicare; consider stopping 6 months before you apply. Source: Medicare.gov, When does Medicare coverage start?. Checked October 25, 2026.

Free one-on-one Medicare counseling in your state. Source: Medicare.gov, Talk to someone; SHIP Technical Assistance Center, Find Local Medicare Help (State Health Insurance Assistance Programs). Checked October 25, 2026.

Medicare's phone line. Source: Medicare.gov, Talk to someone. Checked October 25, 2026.

Every figure on the site, with its source and checked date, is on the sources page.