Medicare · 11 min read
Medicare’s 7-Month Enrollment Window: The Dates, the Exceptions and the Lifetime Part B Penalty
Medicare’s Initial Enrollment Period lasts seven months: the three months before the month you turn 65, that month, and the three after. Missing it without group coverage from current work adds 10 percent of the standard Part B premium, $202.90 in 2026, for each full 12 months of delay, for as long as you have Part B.
Most of the dates around retirement are flexible. Social Security can be claimed in any month between 62 and 70, and a missed tax election can often be repaired later. Medicare enrollment works differently. It runs on fixed windows, the exceptions are specific, and a late start adds a surcharge that stays with the premium for life. None of this is hard to handle once the calendar is laid out, which is the purpose of this guide.
What follows is educational. Enrollment decisions for a specific household, particularly one with employer coverage at 65, should be confirmed with the employer’s benefits office and with Medicare or Social Security directly.
What the Enrollment Question Is Really Asking
“When do I sign up for Medicare?” is really two questions. The first is whether any coverage you hold at 65 lets you postpone Part B without a penalty. The second, if it does not, is which month to enroll so that coverage begins without a gap. Every person turning 65 lands on one of three paths.
| Path | Who uses it | When it runs | Late penalty? |
|---|---|---|---|
| Initial Enrollment Period | Everyone at 65, by default | Seven months centered on the 65th birthday month | No |
| Special Enrollment Period | People covered by a group plan through their own or a spouse’s current work | Eight months for Part B (63 days for Part D) after that work or coverage ends | No |
| General Enrollment Period | Anyone who missed the first window and has no special period | January 1 through March 31 each year | Generally yes |
The rest of this guide takes each path in turn, then prices what a late start costs.
The Initial Enrollment Period, Month by Month
The window opens three months before the month of the 65th birthday, includes the birthday month, and closes at the end of the third month after it. For someone turning 65 in June 2026, it runs from March 1 through September 30, 2026. Enrolling inside it carries no penalty and requires no proof of other coverage.
The month you enroll decides the month coverage begins. Signing up before the birthday month starts coverage on the first day of the birthday month; signing up in the birthday month or later starts it on the first of the following month. (Medicare.gov, when coverage starts)
| Enrollment month (June 2026 birthday) | Coverage begins |
|---|---|
| March, April or May 2026 | June 1, 2026 |
| June 2026 | July 1, 2026 |
| July 2026 | August 1, 2026 |
| August 2026 | September 1, 2026 |
| September 2026 | October 1, 2026 |
Two details shift this schedule. A birthday on the first of a month moves the start of coverage one month earlier. (Medicare.gov, when coverage starts) And anyone already receiving Social Security benefits at least four months before turning 65 is enrolled in Parts A and B automatically, with the Medicare card arriving by mail about three months before coverage begins. (Medicare.gov, getting Social Security before 65) People who have not yet claimed Social Security must sign up themselves.
Part A is usually a simple decision. Most people qualify for it premium-free after 40 quarters of Medicare-covered work, their own or a spouse’s, and take it at 65 even while postponing Part B, subject to the health savings account rule covered below.
The Exception That Works: Coverage From Current Work
One arrangement lets a 65-year-old postpone Part B and Part D without penalty: group health coverage based on current employment, either the individual’s or a spouse’s. When that work or coverage ends, whichever comes first, a Special Enrollment Period opens. (Medicare.gov, working past 65)
- Part B: eight months to enroll.
- Part D: 63 days to join a drug plan.
The exception turns on the word current. The arrangements people most often mistake for qualifying coverage fall outside it.
| Coverage held at 65 | Postpones Part B without penalty? | Who pays first once Medicare-eligible |
|---|---|---|
| Group plan, current job, employer with 20 or more employees | Yes | The group plan |
| Group plan, current job, employer with fewer than 20 employees | Yes, but risky | Medicare |
| COBRA after leaving a job | No | Medicare |
| Retiree health coverage | No | Medicare |
(Medicare.gov, who pays first; Medicare.gov, working past 65)
The third column is where gaps open. When Medicare is the primary payer, the other plan expects Medicare to pay first and may cover only what is left. A person who skipped Part B can find that the plan they relied on pays a fraction of a claim. Medicare notes that retiree coverage might not pay for care during months when someone was eligible for Medicare but had not enrolled, and that COBRA does not extend the time to sign up. (Medicare.gov, who pays first; Medicare.gov, working past 65) Months on COBRA or retiree coverage after the initial window count toward the Part B penalty.
Ask whether the coverage exists because someone is working for that employer today. If the answer is no, as with COBRA or a retiree plan, it does not protect against the late penalty.
Health savings accounts and Part A
Enrolling in any part of Medicare, including premium-free Part A, ends eligibility to contribute to a health savings account from that month forward. (IRS Publication 969) There is a second timing issue. Part A enrollment after 65 can be made retroactive by up to six months, never earlier than the month you turned 65, which is why Medicare advises stopping HSA contributions six months before retiring or applying for Social Security benefits. (Medicare.gov, working past 65)
What a Late Start Costs
Without a qualifying exception, enrolling after the initial window adds separate, permanent surcharges to Part B and Part D. (CMS, 2026 Parts A & B fact sheet; Medicare.gov, avoid late enrollment penalties)
Part B: 10 percent for each full 12-month period
The surcharge is 10 percent of the standard premium for each full 12-month period in which a person could have had Part B and did not. At the 2026 standard premium of $202.90:
| Delay without qualifying coverage | Surcharge | Added each month (2026 premium) | Added each year |
|---|---|---|---|
| 1 full year | 10% | $202.90 × 10% = $20.29 | ≈ $243 |
| 2 full years | 20% | $202.90 × 20% = $40.58 | ≈ $487 |
| 3 full years | 30% | $202.90 × 30% = $60.87 | ≈ $730 |
Medicare rounds the resulting premium to the nearest ten cents. Its own 2026 example: a 20 percent surcharge adds $40.58 to $202.90, for a monthly premium of $243.50. (Medicare.gov, avoid late enrollment penalties)
Two features make the surcharge larger than a single year’s figure suggests. It lasts for as long as the person has Part B. And it is recalculated each year on that year’s standard premium, so the dollar amount rises whenever the premium does. The counting also works in the other direction: because only full 12-month periods count, a delay of eight or ten months may add no surcharge at all, though it can still leave months without coverage.
Part D: 1 percent for each month
The drug-coverage penalty accrues monthly. It equals 1 percent of the national base beneficiary premium for each full month a person was eligible for Part D without creditable drug coverage, and it applies once a gap reaches 63 days. (Medicare.gov, Part D late enrollment penalty) The 2026 base beneficiary premium is $38.99, so each uncovered month adds about $0.39. (CMS, 2026 Part D bid information) Fourteen uncovered months comes to 14 × $0.39 ≈ $5.46, which Medicare rounds to $5.50 a month for 2026, added to the plan premium for as long as the person has drug coverage. (Medicare.gov, Part D late enrollment penalty) There is no 12-month threshold here; every uncovered month counts.
Part A, for those who buy it
People without enough work history for premium-free Part A who enroll late face a separate surcharge: the premium can rise 10 percent, paid for twice the number of years they could have signed up but did not. (Medicare.gov, avoid late enrollment penalties)
10 percent of the standard Part B premium for each full year of delay, recalculated on every future year’s premium and charged for as long as Part B lasts.
If the Window Has Already Closed
A person who missed the initial window and has no Special Enrollment Period can enroll during the General Enrollment Period, January 1 through March 31 of any year. Coverage begins the first day of the month after sign-up. (Medicare.gov, when coverage starts) The late penalties described above generally apply. Reaching this path therefore costs twice: the permanent surcharge, and any months without Part B between the end of the initial window and the next general period.
A Hypothetical Household, Worked Through
This illustration is hypothetical and simplified. It is not based on any client and is not a recommendation for any household. Premium figures use 2026 amounts; actual future premiums will differ.
Consider a single retiree who turns 65 on June 15, 2026. She left her job at 63, has not yet claimed Social Security, and is covered by her former employer’s retiree medical plan, which includes creditable drug coverage. Assuming the retiree plan lets her wait, she does not enroll in Part B. Her initial window closes September 30, 2026.
In late 2027, a large outpatient bill is paid at a fraction of what she expected. Her retiree plan now treats Medicare as the primary payer and covers only its secondary share. She enrolls during the next General Enrollment Period.
| If she enrolls in | Months without Part B after the initial window | Full 12-month periods | Surcharge | Monthly premium at 2026 rates |
|---|---|---|---|---|
| May 2026 (inside the window) | 0 | 0 | None | $202.90 |
| January 2028 (General Enrollment Period) | October 2026 to January 2028: 16 | 1 | 10% | $202.90 + $20.29 = $223.19, rounded to $223.20 |
| January 2029 (General Enrollment Period) | October 2026 to January 2029: 28 | 2 | 20% | $202.90 + $40.58 = $243.48, rounded to $243.50 |
Enrolling in January 2028 starts her Part B on February 1, 2028. Had she enrolled in May 2026, it would have started June 1, 2026, so the late path also left her 20 months, June 2026 through January 2028, with a retiree plan paying as though Medicare had paid first.
The one-year surcharge looks small in a single month. Over 20 years of Part B, $20.29 × 240 months = $4,869.60, before any growth in the standard premium, which the surcharge follows. Her drug coverage produces no Part D penalty, because the retiree plan’s coverage was creditable; had it not been, each uncovered month would have added roughly $0.39 at 2026 rates.
How We Approach This in a Plan
We treat the 65th birthday as a scheduled event in the plan, mapped a year or more in advance, because the Medicare decision touches several others.
- Social Security timing. Claiming benefits at least four months before 65 triggers automatic Part A and B enrollment, and Part B premiums are generally deducted from the benefit once it starts. The claiming decision itself is covered in our Social Security claiming strategy guide.
- Income two years earlier. Medicare’s income-related premiums are generally set from the tax return filed two years before the premium year, (20 CFR §418.1135) so the return for the year someone turns 63 helps price the first year of Medicare. Large conversions, sales or bonuses at 63 deserve that context; see the IRMAA cliff and our broader Medicare and IRMAA guide.
- Roth conversions before 65. Households converting in the years before Medicare need to weigh each conversion’s bracket cost against the premiums it may raise two years later; see Roth conversions: when they pay off.
- Health savings accounts. For anyone still working and contributing, we set the last contribution month against the planned Medicare or Social Security start, including the six-month Part A look-back.
- Premium budgeting. We carry Part B, Part D and supplemental premiums in the retirement cash-flow plan; the 2026 figures are broken out in what Part B costs in 2026.
The output is a dated checklist for each spouse: the window’s opening and closing months, which path applies, who pays first under any employer plan, and the month enrollment should be submitted.
Questions Worth Answering Before You Decide
- In which month does each spouse turn 65, and on what day? A birthday on the first moves the schedule.
- Is any coverage at 65 based on current work, and how many employees does that employer have?
- Has the employer’s benefits office confirmed in writing how its plan coordinates with Medicare?
- Is the drug coverage creditable, and has the plan sent its annual creditable-coverage notice?
- Is anyone contributing to a health savings account, and when should contributions stop?
- When will Social Security be claimed, and will that trigger automatic enrollment?
- What did the tax return from two years before 65 show, and will it raise first-year premiums?
What This Does Not Mean
- It does not mean everyone must enroll in Part B at 65. People covered through current work at a larger employer can generally postpone it without penalty and use the eight-month special period later.
- It does not mean every short delay is penalized. The Part B surcharge counts full 12-month periods, although any delay can leave a coverage gap.
- It does not mean the dollar figures are fixed. The percentages are set by rule; the premiums they multiply change each year.
- It is not personalized advice. The right path depends on employer size, plan terms, drug coverage and HSA status, and should be confirmed with the plan and with Medicare or Social Security.
Frequently Asked Questions
Q: When does Medicare’s seven-month window open and close?
It opens three months before the month you turn 65 and closes at the end of the third month after it. For a June 2026 birthday, the window runs March 1 through September 30, 2026.
Q: How much is the Part B late enrollment penalty in 2026?
10 percent of the standard premium for each full 12-month period of delay without qualifying coverage. One year adds $20.29 to the 2026 premium of $202.90; two years add $40.58. The surcharge lasts as long as you have Part B.
Q: Does COBRA or retiree coverage let me delay Part B without a penalty?
No. Only group coverage based on your own or a spouse’s current employment qualifies. Months on COBRA or retiree coverage after the initial window count toward the penalty, and Medicare generally pays first alongside either one.
Q: I am still working at 65. Do I need Part B?
Coverage through current work generally lets you postpone Part B and use an eight-month Special Enrollment Period (63 days for Part D) when the work or coverage ends. At employers with fewer than 20 employees, Medicare generally pays first, so delaying can leave large gaps.
Q: When does coverage start if I sign up during the window?
Signing up before your birthday month starts coverage on the first of your birthday month. Signing up in the birthday month or later starts it on the first of the following month.
Q: How is the Part D late penalty calculated?
1 percent of the national base beneficiary premium, $38.99 in 2026, for each full month without creditable drug coverage once a gap reaches 63 days. Fourteen months adds about $5.46, which Medicare rounds to $5.50 a month.
Bring the decision in front of you.
The first conversation is 30 minutes. A recent statement helps; no preparation is needed.
Sources and further reading
- CMS, 2026 Medicare Parts A & B Premiums and Deductibles
- CMS, 2026 Part D bid information (base beneficiary premium)
- Medicare.gov, avoid late enrollment penalties
- Medicare.gov, Part D late enrollment penalty
- Medicare.gov, when does Medicare coverage start
- Medicare.gov, getting Social Security before 65
- Medicare.gov, working past 65
- Medicare.gov, who pays first
- IRS Publication 969
- 20 CFR §418.1135
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The views and opinions expressed here are those of The Financial Sciences Company as of the publish date and are provided for informational and educational purposes only. They are not personalized investment, tax, or legal advice. The Financial Sciences Company, LLC is a registered investment adviser. Registration does not imply a certain level of skill or training. Additional information is available in our Form ADV at adviserinfo.sec.gov.
General educational information, current as of 2026. Figures and rules change. For guidance specific to your situation, speak with a qualified professional.