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.
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The three enrollment windows
| Window | When | What it covers |
|---|---|---|
| Initial enrollment | 3 months before through 3 months after your 65th birthday month | Your first chance. Seven months total. |
| Special enrollment | While covered by a current employer, and 8 months after that ends | Lets you delay without penalty if you qualify |
| General enrollment | January 1 to 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 and 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 the 2026 standard premium of $202.90 (CMS, 2026), that is $60.87 a month, about $730 a year, and the dollar amount grows as the premium rises (Medicare.gov, late enrollment penalties).
The Part D penalty works the same way on a smaller number. In 2026 the national base premium is $38.99. Go 24 months without creditable drug coverage and the penalty is 24% of that, about $9.40 a month added to your plan premium for as long as you have drug coverage.
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, so enroll at 65 |
| COBRA or retiree coverage | Does not count as current employer coverage. Enroll at 65. |
| Marketplace (ACA) plan | Does not count. Enroll at 65. |
| Contributing to an HSA | Medicare enrollment 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 of $202.90 a month in 2026 (CMS), and if your income is above the IRMAA line ($109,000 single or $218,000 joint on your 2024 return) 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 enroll 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, because 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. Your working shows right away, free. Enter your email to see the exact dollars.
| Provisional income | $0 |
| Which tier you land in | n/a |
| 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.
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Sources: Medicare.gov, when coverage starts; Medicare.gov, avoid late enrollment penalties; Medicare.gov, working past 65; CMS, 2026 Medicare Parts A and B premiums and deductibles. Checked October 10, 2026. Education only. Rules for your own employer plan can differ, so confirm with Medicare (1-800-633-4227) or Social Security before you delay.
Common questions
When should I enroll in Medicare?
Your initial enrollment 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 enrollment 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 enroll 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 one exception is the Social Security taxation thresholds, which have not moved since 1983 and are not expected to.
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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.
Hans Goldstein, EA
Founder & Executive Director · Retirement Literacy Foundation, a 501(c)(3) non-profit
Admitted to practice before the IRS
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