When do you apply for Medicare?

Key points

• Most people apply in their Initial Enrollment Period: the 7 months that start 3 months before the month they turn 65 and end 3 months after it.
• If you already get Social Security or Railroad Retirement Board benefits, you are enrolled in Part A and Part B automatically from the month you turn 65. Otherwise you have to apply, and full retirement age for Social Security does not change that: Medicare still starts at 65.
• If you or your spouse are still working and covered by that job’s health plan, you can usually wait to take Part B without a penalty, and sign up within 8 months of the job or the coverage ending.
• COBRA and retiree coverage do not count as coverage from current work. Waiting on either can mean a gap in coverage and a Part B penalty that lasts as long as you have Part B.

The rules are federal and fairly mechanical. The hard part is knowing which of three windows applies to you. This guide walks through them in the order most people meet them. It is part of our Medicare guide, which covers costs and the other decisions around 65.

Are you enrolled automatically?

It depends on whether you already get Social Security or Railroad Retirement Board benefits when you reach 65.

Your situation at 65	What happens
Already getting Social Security or RRB benefits	Part A and Part B start automatically on the first day of the month you turn 65. Your Medicare card arrives about 3 months before your birthday
Not getting Social Security or RRB benefits yet	Nothing happens automatically. You apply through Social Security

If you are enrolled automatically, you keep Part B unless you tell Social Security before the coverage start date on your card. If you do nothing, Part B stays and its premium comes out of your benefit. That matters if you are still working with good employer coverage, because you may not want to pay for Part B yet (see below).

Full retirement age for Social Security is no longer 65, so many people reach 65 before they claim, which leaves them outside automatic enrollment. Social Security’s own Medicare booklet says to sign up three months before your 65th birthday even though full retirement age is no longer 65, and even if you do not plan to retire at 65. For the Social Security side of that decision, see our guide to full retirement age.

Your Initial Enrollment Period: the 7 months around 65

Your first chance to sign up is the Initial Enrollment Period. It lasts 7 months: the 3 months before the month you turn 65, that month, and the 3 months after. If your birthday falls on the first of a month, the whole window starts and ends a month earlier.

When coverage starts depends on when in the window you sign up:

You sign up	Coverage starts
In the 3 months before the month you turn 65	The first day of your birthday month
In the month you turn 65 or the 3 months after	The first day of the month after you sign up

Worked example (hypothetical). Someone born on August 20, 1962 turns 65 on August 20, 2027.

Sign up in	Coverage starts
May, June or July 2027	August 1, 2027
August 2027	September 1, 2027
September 2027	October 1, 2027
October 2027	November 1, 2027
November 2027	December 1, 2027

Their window runs from May 1 to November 30, 2027. Signing up early, in May, June or July, means no gap. Had they been born on August 1, 1962, the window would run from April to October 2027, and signing up in April, May or June would start coverage on July 1, 2027.

You can join a Medicare Advantage plan or a drug plan in the same window. If you ask to join before Part A or Part B starts, the plan starts the same day they do.

Can you delay Medicare if you are still working?

Often, yes, for Part B. The test is whether you have group health plan coverage based on current employment, your own or your spouse’s.

If you do, you can sign up for Part A and Part B:

• any time you are still covered by that plan, or
• during the 8 months that begin the month after the job ends or the coverage ends, whichever happens first.

Social Security describes the same window this way: within 8 months of the day you or your spouse stop working, even if the group plan continues for a time. Sign up in that window and you usually pay no late penalty. Coverage generally starts the month after you sign up. If you sign up while you are still working, or in the first full month after the coverage ends, you can ask for Part B to start up to 3 months later.

Part A is different. If you qualify for premium-free Part A (usually after 10 years of work paying Medicare taxes, yours or a spouse’s), you can sign up any time after you first become eligible. When you do, Part A starts up to 6 months back from the month you apply, but never before the month you first became eligible. That backdating matters if you have a health savings account, below.

Two cautions. If the employer has fewer than 20 employees, Medicare usually pays first and the employer plan second, so delaying Part B can leave bills unpaid even though no penalty applies. And ask the plan before you skip Part B: if you do not sign up for Part A and Part B, your job-based insurance might not cover the costs. Our guide on Medicare when you have employer insurance covers who pays first.

Coverage that does not let you wait

Medicare is specific about what is not active employer coverage:

• COBRA, or similar continuation coverage after the job ends
• retiree coverage
• VA coverage
• individual coverage, such as a Marketplace plan
• former-employer coverage through severance or a layoff

COBRA does not qualify you for the Special Enrollment Period, and COBRA ending does not open one. The 8 months run from the end of the job-based coverage whether or not you take COBRA. Retiree coverage may not pay for your health services if you do not have both Part A and Part B. Our guide to COBRA and Medicare goes through the timing.

If you have a Marketplace plan, Medicare tells you to sign up when you are first eligible and to end the Marketplace plan before Medicare starts, so they do not overlap. Once you are eligible for premium-free Part A, you no longer qualify for Marketplace help with premiums.

There is also a Special Enrollment Period for exceptional situations, such as a natural disaster or emergency, incarceration, an employer or health plan error, or losing Medicaid. Social Security’s form for it is CMS-10797.

Missed your window? The General Enrollment Period

If you missed your Initial Enrollment Period and do not qualify for a Special Enrollment Period, you can sign up for Part B from January 1 to March 31 each year. Since 2023, coverage starts the month after you sign up. Medicare Open Enrollment in the autumn (October 15 to December 7) is a different window: it is for choosing health and drug plans, not for signing up for Part B.

Waiting usually costs money. The Part B late enrollment penalty adds 10% to your premium for each full 12 months you could have had Part B but did not, and you pay it for as long as you have Part B. The months are counted from the end of your Initial Enrollment Period through the month you sign up. Months when you were 65 or older and covered by an employer plan through your own or your spouse’s current work are left out.

Worked example (hypothetical). Someone’s Initial Enrollment Period ended on September 30, 2025. They had no employer coverage, and they sign up for Part B in the General Enrollment Period in February 2027, so coverage starts March 1, 2027.

• October 2025 through February 2027 is 17 months: 1 full 12-month period, so a 10% penalty.
• At the 2026 standard premium of $202.90, that is $202.90 x 1.10 = $223.19, billed as $223.20, or $20.30 a month more ($243.60 a year).
• CMS had not published the 2027 Part B premium when we checked on November 4, 2026, so the 2027 bill will be 10% above whatever the 2027 standard premium turns out to be.

We checked the method against Medicare.gov’s own example: a 20% penalty on the 2026 premium is $40.58, for $243.48 in total, billed as $243.50 after rounding to the nearest $0.10. The full rules, including the Part A and Part D penalties, are in our guide to the Medicare late enrollment penalty.

How to apply for Medicare

You sign up for Part A and Part B through Social Security, not Medicare.gov.

• Online: if you are 65 or older, at https://www.ssa.gov/medicare/sign-up, for Parts A and B or Part A only.
• By phone: 1-800-772-1213 (TTY 1-800-325-0778).
• At a Social Security office: by appointment.

If you already have Part A and are adding Part B after employer coverage ends, you can apply online during the Special Enrollment Period, or fax or mail Form CMS-40B with Form CMS-L564 (Request for Employment Information). CMS-L564 is the proof that your coverage came from current work: you fill in Section A and your employer fills in Section B. Coverage generally begins the month after you sign up, so Medicare suggests signing up about a month before your employer coverage ends to avoid a gap.

What else to time at 65

A health savings account. You cannot contribute to an HSA once you have Medicare. The IRS sets your contribution limit at zero from the first month you are enrolled, including months of backdated Part A. Medicare.gov says you and your employer should stop contributing 6 months before you retire or apply for Social Security benefits, and Social Security’s Medicare booklet says to stop at least 6 months before you apply for Medicare, because Part A can start up to 6 months back. You can still spend the money already in the account.

Drug coverage. If your current drug coverage is creditable, meaning expected to pay on average at least as much as standard Part D, you can wait to join a Medicare drug plan. Your plan has to tell you whether it is creditable. Go 63 days or more in a row without creditable coverage after your Initial Enrollment Period and a Part D penalty applies: 1% of the national base beneficiary premium ($41.33 in 2027) for each full month without coverage, for as long as you have Part D. Our guide to what Medicare Part D costs has the details.

Medigap. Your federal Medigap Open Enrollment Period is the 6 months that start the first month you have Part B and are 65 or older. Outside that window, and outside the situations Medicare calls “guaranteed issue rights,” an insurer does not have to sell you a policy and may charge more because of your health. Some states give more rights. Starting Part B starts that 6-month clock, which is one more reason to time Part B carefully. See Medigap vs Medicare Advantage.

Where to get free help

State Health Insurance Assistance Programs (SHIPs) give free, personalized Medicare counseling and are not connected to any insurance company or plan. Find yours at shiphelp.org or through 1-800-MEDICARE (1-800-633-4227, TTY 1-877-486-2048), which is open 24 hours a day, 7 days a week. For questions about enrollment in Part A and Part B, call Social Security at 1-800-772-1213.

About this guide

Written by the Diversify Guy editorial desk. Diversify Guy is a pen name. It is the byline of our editorial team, not a single individual. We do not publish personal trading records or claim to be your adviser. We tell you where every figure came from so you can check it yourself. How we work and how we get paid.

This guide explains federal Medicare rules; some states add their own rules for Medigap and other coverage. It is not personalized insurance, tax, legal or financial advice. Diversify Guy earns affiliate commissions and advertising fees from companies featured elsewhere on the site. This page carries no ads and no affiliate links.

Sources and check dates

All sources checked on November 4, 2026.

• Medicare & You 2027, the official handbook (automatic enrollment, the enrollment periods, Special Enrollment Period, COBRA and retiree coverage, Part A backdating, the Part B penalty and its example, Marketplace coverage): https://www.medicare.gov/publications/10050-medicare-and-you.pdf
• Medicare.gov, when Medicare coverage starts: https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
• Medicare.gov, working past 65: https://www.medicare.gov/basics/get-started-with-medicare/medicare-basics/working-past-65
• Medicare.gov, avoid late enrollment penalties (2026 Part B penalty example): https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
• Medicare.gov, joining a plan: https://www.medicare.gov/basics/get-started-with-medicare/get-more-coverage/joining-a-plan
• Medicare.gov, when you can buy Medigap: https://www.medicare.gov/health-drug-plans/medigap/ready-to-buy/when
• Medicare.gov, how Medicare works with other insurance (publication 02179: who pays first, retiree coverage, SHIP): https://www.medicare.gov/publications/02179-how-medicare-works-with-other-insurance.pdf
• CMS, press release on the 2027 plan year and Open Enrollment (1-800-MEDICARE hours): https://www.cms.gov/newsroom/press-releases/medicare-advantage-medicare-prescription-drug-programs-expected-remain-stable-2027
• Social Security, sign up for Medicare: https://www.ssa.gov/medicare/sign-up
• Social Security, sign up for Part B only (forms CMS-40B, CMS-L564, CMS-10797): https://www.ssa.gov/medicare/sign-up/part-b-only
• Social Security, when to sign up for Medicare: https://www.ssa.gov/medicare/plan/when-to-sign-up
• Social Security, Medicare booklet (publication 05-10043): https://www.ssa.gov/pubs/EN-05-10043.pdf
• CMS, Form CMS-L564 (Request for Employment Information): https://www.cms.gov/medicare/cms-forms/cms-forms/cms-forms-items/cms009718
• Social Security POMS HI 01001.010, premium increase for late enrollment: https://secure.ssa.gov/poms.nsf/lnx/0601001010
• IRS Publication 969, health savings accounts (Medicare and the contribution limit): https://www.irs.gov/publications/p969
• CMS, 2026 Medicare Parts A and B premiums and deductibles fact sheet: https://www.cms.gov/newsroom/fact-sheets/2026-medicare-parts-b-premiums-deductibles
• CMS address for the 2027 Part B fact sheet, which returned “Page Not Found” on November 4, 2026: https://www.cms.gov/newsroom/fact-sheets/2027-medicare-parts-b-premiums-deductibles
• CMS, Part D 2027 base beneficiary premium: https://www.cms.gov/newsroom/fact-sheets/medicare-part-d-2027-national-average-monthly-bid-amount-information
• 42 CFR 406.24, 407.14, 407.15, 407.20 and 407.25 (enrollment periods, Special Enrollment Period, coverage start): https://www.ecfr.gov/current/title-42/section-406.24, https://www.ecfr.gov/current/title-42/section-407.14, https://www.ecfr.gov/current/title-42/section-407.15, https://www.ecfr.gov/current/title-42/section-407.20 and https://www.ecfr.gov/current/title-42/section-407.25
• 42 CFR 408.22 and 408.24 (Part B premium increase for late enrollment): https://www.ecfr.gov/current/title-42/section-408.22 and https://www.ecfr.gov/current/title-42/section-408.24
• 42 CFR 423.46 and 423.286 (Part D late enrollment penalty and its amount): https://www.ecfr.gov/current/title-42/section-423.46 and https://www.ecfr.gov/current/title-42/section-423.286
• 42 CFR 422.62 and 423.38 (the October 15 to December 7 Open Enrollment window): https://www.ecfr.gov/current/title-42/section-422.62 and https://www.ecfr.gov/current/title-42/section-423.38
• CMS, 2026 Part D bid information (2026 base beneficiary premium): https://www.cms.gov/newsroom/fact-sheets/2026-medicare-part-d-bid-information-and-part-d-premium-stabilization-demonstration-parameters