When to Enroll in Medicare
This is one of the few retirement deadlines with a permanent, compounding cost for missing it. Most other mistakes can be corrected. This one follows you.
The three enrolment windows
| Window | When | What it covers |
|---|---|---|
| Initial enrolment | 3 months before through 3 months after your 65th birthday month | Your first chance. Seven months total. |
| Special enrolment | While covered by a current employer, and 8 months after that ends | Lets you delay without penalty if you qualify |
| General enrolment | January 1 – March 31 each year | The fallback if you missed the others. Penalties usually apply. |
Enrolling in the three months before your birthday month starts coverage on the first of your birthday month. Enrolling later delays the start, which can leave a gap.
The penalty, concretely
Part B: 10% added for each full 12-month period you could have enrolled and did not. It is permanent — it does not fall off after a few years.
Part D: roughly 1% of the national base premium for each month without creditable drug coverage. Also permanent.
Delay Part B by three years without qualifying coverage and you pay 30% more every month for the rest of your life. On a $200 premium that is $60 a month, forever, indexed upward as premiums rise.
Still working at 65?
This is where most of the confusion sits, and the answer depends on employer size.
| Your situation | What usually applies |
|---|---|
| Employer with 20+ employees, you are covered | You can generally delay Part B without penalty |
| Employer with fewer than 20 | Medicare typically pays first — enrol at 65 |
| COBRA or retiree coverage | Does not count as current employer coverage. Enrol at 65. |
| Marketplace (ACA) plan | Does not count. Enrol at 65. |
| Contributing to an HSA | Medicare enrolment ends HSA contributions. Plan the timing. |
The COBRA trap catches people every year. It feels like coverage, and it is — but not the kind that protects you from the Part B penalty.
What it will cost
Most people pay no premium for Part A because they paid in for 40 quarters. Part B has a standard premium, and if your income is above the IRMAA threshold you pay a surcharge on top — based on your tax return from two years ago.
That lookback is why a one-time income event at 63 can raise your Medicare premium at 65. A large Roth conversion, a home sale, or a final big working year all land in the year Medicare will eventually look at.
What to do, in order
- Mark the seven-month window and enrol in the first three months if you are not covered by a large employer.
- Confirm your coverage counts if you plan to delay. Ask HR in writing whether the plan is based on current employment and how many employees the company has.
- Stop HSA contributions six months before enrolling — Part A can backdate.
- Look at the income two years ahead. The year that sets your first IRMAA determination is the one you are living in at 63.
Check your own number
Three inputs, instant answer, nothing gated. The email step afterwards is optional.
| Provisional income | $0 |
| Which tier you land in | — |
| Share of benefit taxed | 0% |
We will email you a written copy showing how the math worked, what would change your tier, and the thresholds for next year. Free, and you can keep it or forward it to whoever does your taxes.
Educational follow-up by email. We never sell your information.
Common questions
When should I enrol in Medicare?
Your initial enrolment period runs seven months: the three months before your 65th birthday month, the birthday month itself, and the three months after. Enrolling in the first three months starts coverage on the first day of your birthday month.
What is the Medicare late enrolment penalty?
Part B adds 10% for every full 12-month period you could have enrolled and did not, and the penalty is permanent. Part D adds roughly 1% of the national base premium for each month without creditable drug coverage, also permanently.
Can I delay Medicare if I am still working at 65?
Usually yes if you are covered by a current employer with 20 or more employees. If the employer has fewer than 20 employees, Medicare typically pays first and you should enrol at 65. COBRA, retiree coverage and marketplace plans do not count as current employer coverage.
Does COBRA count as coverage for delaying Medicare?
No. COBRA is not considered current employer coverage for Medicare purposes. Relying on it to delay Part B is one of the most common and most expensive mistakes, because the late penalty is permanent.
Why is my Medicare premium based on income from two years ago?
IRMAA uses a two-year lookback, so your 2026 premium is set by your 2024 tax return. A one-time event such as a home sale or Roth conversion at 63 can raise the premium you pay at 65.
Can I keep contributing to my HSA after enrolling in Medicare?
No. HSA contributions must stop once Medicare begins. Because Part A can be backdated up to six months, most people stop contributing about six months before enrolling to avoid an excess-contribution problem.
These numbers change every year
The IRMAA brackets, the standard deduction and the senior deduction are all adjusted annually, and the 2027 figures are published late in 2026. The Social Security taxation thresholds are the one exception — those have not moved since 1983 and are not expected to.
We send one short email when the new numbers are announced. No campaign, no sequence — one email when there is something worth knowing.
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Will your income trigger an IRMAA surcharge?
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Check the IRMAA bracketsRelated guides
How to Avoid IRMAAThe moves that keep you under the line.What Is Provisional Income?The number that decides how much gets taxed.How to Reduce Taxes on Your Social SecurityFive levers that lower provisional income.The Retirement Literacy Foundation is a 501(c)(3) non-profit. This guide is general financial education, not individualized investment, tax, or insurance advice. Tax rules change and depend on your personal situation. Consider speaking with a licensed professional before making decisions.