Medicare at 65: The Enrollment Windows That Cost People for Life

Almost every expensive Medicare mistake is a calendar mistake. Not choosing the wrong plan — missing a window. And the penalties attached to those windows are not one-off fines: several of them raise your premium every month for the rest of your life.

There are four windows around turning 65. Three of them can cost you permanently.

Window 1: your Initial Enrollment Period

Seven months: the three months before the month you turn 65, that month, and the three months after.

Within that window, when you act still matters. Sign up in the first three months and coverage begins on the first day of your birthday month. Sign up in your birthday month or later and coverage is pushed back — you can end up with weeks or months uninsured for no reason other than timing.

If you are already receiving Social Security when you approach 65, you are enrolled in Parts A and B automatically, and the card arrives in the mail. Everyone else has to act. Nobody will chase you.

Window 2: the Special Enrollment Period, if you are still working

If you are covered by a group health plan based on current employment — yours or your spouse’s — you can delay Part B without penalty. When that employment or coverage ends, an 8-month Special Enrollment Period begins.

This is where the expensive mistake lives. “Current employment” means someone is actively working. COBRA is not current employment coverage. Retiree coverage is not either. People take COBRA at 65, believe they are covered, and discover eighteen months later that the clock has been running the whole time — leaving them with a permanent Part B penalty and a wait for coverage to start.

One more trap: if the employer has fewer than 20 employees, Medicare usually becomes the primary payer at 65. The group plan then pays only what Medicare does not — so if you have not enrolled in Medicare, large parts of a claim can go unpaid. Ask the employer’s benefits administrator, in writing, whether their plan is primary or secondary once you turn 65.

Window 3: Medigap open enrollment — the one nobody mentions

Original Medicare has no out-of-pocket maximum. A serious illness is theoretically unlimited exposure, which is why most people add either a Medigap (Medicare Supplement) policy or a Medicare Advantage plan.

Your Medigap open enrollment period is six months, beginning the month you are both 65 and enrolled in Part B. During it you have guaranteed issue rights: any insurer selling Medigap in your state must sell you any policy they offer, at the standard price, regardless of your health history.

After those six months, in most states, Medigap insurers may use medical underwriting — they can charge you more, exclude conditions, or refuse to sell you a policy at all. This window does not come back, and it is not announced. A diagnosis at 67 can leave someone permanently unable to buy the supplement they assumed they could add later.

A few states — Connecticut, Massachusetts, Maine and New York among them — require guaranteed issue year-round or annually. Most do not. This is a state-specific fact worth confirming before you decide to wait.

Window 4: Part D, even if you take no medication

The commonest reasoning is: “I take nothing, so I will skip drug coverage.” It is also the commonest way to acquire a lifelong surcharge.

The Part D late enrollment penalty is 1% of the national base beneficiary premium for every full month you went without creditable drug coverage, added to your premium permanently and recalculated each year. Someone who waits five years pays roughly 60% extra, for life.

Enrolling in the cheapest available Part D plan while healthy is, in effect, buying insurance against the penalty. If you have other drug coverage, get written confirmation from that plan that it is creditable — that word is what protects you.

What the penalties actually cost

Penalty	How it is calculated	How long
Part B late enrollment	+10% of the standard premium for each full 12 months you could have had Part B and did not	For as long as you have Part B — normally life
Part D late enrollment	+1% of the national base beneficiary premium per uncovered month	For as long as you have Part D
Part A late enrollment	+10%, if you have to buy Part A	Twice the number of years you delayed

At the 2026 standard Part B premium of $202.90 a month, a two-year delay adds about $40 every month, indefinitely. Over a twenty-year retirement that is roughly ten thousand dollars for a missed form.

The 2026 numbers

Item	2026
Part B standard monthly premium	$202.90
Part B annual deductible	$283
Part A hospital deductible, per benefit period	$1,736
Part A coinsurance, hospital days 61–90	$434 a day
Part A coinsurance, lifetime reserve days	$868 a day
Skilled nursing facility, days 21–100	$217 a day
Part A premium	$0 for about 99% of people

Published by the Centers for Medicare & Medicaid Services each fall for the following calendar year. Current figures: Medicare costs at a glance.

Higher earners pay an income-related surcharge (IRMAA) on Parts B and D, based on the tax return from two years earlier. If your income has since fallen because of retirement, divorce or bereavement, you can ask for the surcharge to be recalculated using form SSA-44 — a form a great many newly retired people are entitled to file and never hear about.

If money is tight, ask about these first

• Medicare Savings Programs — state-run programs that pay your Part B premium, and sometimes deductibles and coinsurance too. Income limits are higher than people expect and several states have removed the asset test. Qualifying also enrolls you automatically in Extra Help.
• Extra Help (the Part D Low-Income Subsidy) — cuts drug costs to a few dollars a prescription and waives the Part D late penalty.
• Full Medicaid alongside Medicare — “dual eligible” status, which covers most of what Medicare leaves behind.

Apply for Medicare Savings Programs through your state Medicaid agency, and for Extra Help through Social Security.

The HSA trap

If you contribute to a Health Savings Account and plan to keep working past 65, stop contributing six months before you enroll in Medicare. Part A can be granted retroactively for up to six months, and contributions made during a month you were retroactively covered are excess contributions, subject to tax and penalty. Enrolling in Social Security at 65 triggers Part A automatically, which triggers this.

A timeline that works

• Six months before 65 — if you have an HSA, stop contributing. Ask your employer, in writing, whether their plan stays primary after 65.
• Four months before — book free counseling with your State Health Insurance Assistance Program. It is independent, free, and not selling anything.
• Three months before — enroll, unless you have genuine current-employment coverage. Apply at SSA.gov.
• The month Part B starts — the Medigap clock begins. Decide between Medigap plus Part D and Medicare Advantage now, not later.
• Every October to December — Medicare Open Enrollment, October 15 to December 7. Drug plan formularies change annually; re-check yours against the medicines you actually take.

SHIP counselors are the single best resource here. They are trained, independent of insurers, and free — and unlike a broker, they are not paid a commission on what you choose. Find yours at shiphelp.org.