Turning 65: A Medicare Checklist, Month by Month

Your window: the Initial Enrollment Period

The first chance to sign up is called the Initial Enrollment Period (IEP). Medicare.gov describes it as seven months, starting three months before you turn 65 and ending three months after the month you turn 65. If your birthday falls on the 1st, Medicare treats you as reaching 65 a month earlier, so the whole window moves back a month.

Source: Medicare.gov, When does Medicare coverage start? Rule in effect for 2026 and 2027.

Premium-free Part A starts the month you turn 65 if you qualify. The lesson from the table is simple: if you want Medicare to begin the day your birthday month begins, and you are not being enrolled automatically, sign up in the three months before it.

The checklist, month by month

Six months before your birthday month

• Find your 65th-birthday month and write down your 7-month window.
• Check whether you already receive Social Security or Railroad Retirement benefits. If you do, enrollment in Parts A and B is automatic.
• If you or your spouse are still working, ask the benefits office how many employees the employer has and whether its drug coverage is creditable. Get the answer in writing.
• Make a list of your doctors, clinics and hospitals, and every prescription with its dose. You will need both lists to compare plans.

Three months before

• If you are not enrolled automatically, apply for Parts A and B through Social Security. Medicare.gov lists the ways: online, by phone at 1-800-772-1213 (TTY 1-800-325-0778), or at a local office.
• If you are on Social Security already, watch the mail for your Medicare card. The CMS handbook says it comes about 3 months before your 65th birthday.
• Decide between Original Medicare with a Medigap policy and a drug plan, or a Medicare Advantage plan. Our guide to Medicare Advantage vs Medigap walks through the trade-off.

Your birthday month

• Confirm your Medicare card shows the right start dates for Part A and Part B.
• If you chose a Medicare Advantage or drug plan, confirm the plan's start date and that your pharmacy has your new card.
• If you are buying Medigap, apply now: your Medigap open enrollment has started if you are 65 and enrolled in Part B.

The months after

• Book your Welcome to Medicare preventive visit. The CMS handbook says it is available within the first 12 months you have Part B.
• Keep the yearly creditable-coverage notice from any employer drug plan you stay on.
• Mark October 15 to December 7 on your calendar. That is Open Enrollment, when you can change plans for the next year.

If you, or your spouse, are still working

The size of the employer decides a lot. The CMS Medicare & You 2027 handbook explains that if the employer has 20 or more employees, the group plan generally pays first and Medicare second. With fewer than 20, Medicare pays first, and the group plan may pay very little unless you have both Part A and Part B.

If you delay Part B because of current-employment coverage, you get a Special Enrollment Period of 8 months after the job or the coverage ends, whichever comes first. COBRA does not extend it. Many people take premium-free Part A at 65 even while working, but if you contribute to a Health Savings Account, note that Medicare.gov says premium-free Part A starts up to 6 months back from when you sign up, which affects when your HSA contributions have to stop. Our guide to working past 65 goes into this in detail.

Medigap timing in South Dakota

A Medicare Supplement, or Medigap, policy helps pay the deductibles and coinsurance Original Medicare leaves to you. Federally, your Medigap Open Enrollment Period lasts 6 months, starting the first month you are 65 or older and enrolled in Part B, according to Medicare.gov.

The South Dakota Division of Insurance states the same rule on its Medicare supplement page: there is a six-month open enrollment period once you reach 65, and during it a Medicare supplement policy can be obtained regardless of your health. The Division adds that people under 65 who qualify for Medicare because of a disability also have a six-month open enrollment period, beginning on the date of their Part B enrollment.

Outside that window, and outside the specific guaranteed-issue situations federal law lists, insurers can ask health questions. That is why the order matters: if you delay Part B because you are working, your Medigap window waits too, and starts when Part B does. For South Dakota's Medigap plans in more depth, see our existing South Dakota Medigap guide.

Do not forget drug coverage

Parts A and B do not cover most prescriptions you fill at a pharmacy. That is the job of Part D, either a stand-alone plan alongside Original Medicare or drugs built into a Medicare Advantage plan. If you go 63 days or more in a row without Part D or other creditable coverage after your IEP ends, the CMS handbook says a late enrollment penalty can follow you for as long as you have drug coverage.

For 2027, Medicare.gov's drug costs page lists a cap of $2,400 on what you pay out of pocket for covered drugs in a year. Before you choose, check each prescription on the plan's list of covered drugs; our guide on checking doctors and drugs before you choose shows how, using Medicare Plan Finder.

What the first year costs

For 2026, the standard Part B premium is $202.90 a month and the Part B deductible is $283, according to the CMS 2026 fact sheet. CMS had not announced the 2027 amounts when we checked on October 19, 2026. Higher earners pay more under IRMAA, which looks at your tax return from two years earlier; for 2026 that starts above $109,000 of income for an individual or $218,000 for a joint return. See our guide to IRMAA, and our existing Medicare costs breakdown for the rest.

Figures and sources

Every figure on this page, where it comes from, and the period it covers. Checked October 19, 2026.

Official sources

• Medicare.gov: When does Medicare coverage start?
• Medicare.gov: How do I sign up for Medicare?
• CMS: Medicare & You 2027 handbook
• Medicare.gov: When can I buy Medigap?
• South Dakota Division of Insurance: Medicare Supplement Policies
• Medicare.gov: Costs for Medicare drug coverage
• Medicare.gov: Joining a health or drug plan
• CMS: 2026 Medicare Parts A & B Premiums and Deductibles

How this guide is made: the Big Sioux Benefits Data Desk writes from official sources and checks each figure against the page it cites. This is general education, not advice about your situation. Plan details vary; confirm costs and coverage with Medicare.gov, the agency named above, or a licensed agent.