Medicare at 65, When to Sign Up and How the Part B Penalty Works
Your Medicare Initial Enrollment Period lasts 7 months around your 65th birthday, and missing it can add 10% to your Part B premium for each full 12 months you were late, usually for life. As of October 2026, the standard Part B premium is $202.90 a month for 2026, per CMS.
1. Your first window: the Initial Enrollment Period
Medicare.gov explains that your first chance to sign up is generally around your 65th birthday. This Initial Enrollment Period lasts 7 months: it starts 3 months before the month you turn 65, includes your birthday month, and ends 3 months after it.
1.1. When coverage begins
Coverage always starts on the first of a month. According to Medicare.gov:
- If you qualify for premium-free Part A, Part A starts the month you turn 65. If your birthday is on the first of the month, it starts the month before.
- For Part B, the start date depends on when you sign up:
| If you sign up for Part B | Coverage starts |
|---|---|
| Before the month you turn 65 | The month you turn 65 |
| The month you turn 65, or in the 3 months after | The next month |
So signing up in the three months before your birthday month avoids any gap.
2. If you miss it: the General Enrollment Period
After your Initial Enrollment Period ends, Medicare.gov says you can generally sign up for Part B only during another enrollment period. The General Enrollment Period runs January 1 to March 31 each year, and coverage starts the month after you sign up. You may also owe a late enrollment penalty if you do not qualify for a Special Enrollment Period.
3. The big exception: coverage from a current job
Many people work past 65. Medicare.gov describes a Special Enrollment Period for people who have or had health insurance through their own job or a spouse's job:
- It starts the first month after your Initial Enrollment Period ends.
- It ends 8 months after the group health plan coverage or the employment ends, whichever happens first.
- If you sign up while still working, or within the first full month after employer coverage ends, you can ask to delay your Part B start date by up to 3 months.
The guidance on penalties says that generally you will not pay a Part B penalty if you qualify for a Special Enrollment Period. The safe habit is to mark the date your job or employer coverage ends and count 8 months from the earlier one.
Medicare.gov lists other Special Enrollment Periods as well, for situations such as losing Medicaid, a declared disaster, or receiving inaccurate information from a health plan or employer.
4. How the Part B penalty works
Medicare.gov describes late enrollment penalties as:
- added to your monthly premium, not a one-time fee,
- usually charged for as long as you have that coverage, which for most people means for life,
- larger the longer you wait.
For Part B specifically, you pay an extra 10% for each full 12-month period you could have signed up but did not.
4.1. The 2026 numbers
CMS set the 2026 standard Part B premium at $202.90 a month, up $17.90 from $185.00 in 2025. The annual Part B deductible for 2026 is $283.
Medicare.gov's own example: waiting 2 full years means a 20% penalty. For 2026 that is $202.90 plus $40.58, or $243.48, rounded to $243.50 a month.
Here is the same calculation across different delays, using the 2026 standard premium:
| Full years late | Penalty | Monthly penalty (2026) | Extra cost per year |
|---|---|---|---|
| 1 | 10% | $20.29 | $243.48 |
| 2 | 20% | $40.58 | $486.96 |
| 3 | 30% | $60.87 | $730.44 |
| 5 | 50% | $101.45 | $1,217.40 |
Because the penalty is a percentage of the premium, it rises when the premium rises. And because it usually lasts for life, a 20% penalty paid for 20 years at today's premium would add more than $9,700, before any premium increases.
5. Part A and Part D have their own rules
- Part A: most people get it premium-free. CMS says about 99% of beneficiaries have no Part A premium. If you must buy Part A and sign up late, Medicare.gov says the premium may go up 10%, paid for twice the number of years you did not sign up.
- Part D (drug coverage): Medicare.gov says the penalty is 1% of the national base beneficiary premium for each month you went without drug coverage or creditable coverage, if the gap was 63 days or more. The 2026 national base beneficiary premium is $38.99.
6. A simple timeline to follow
- About 4 months before your 65th birthday: decide whether you will keep employer coverage or start Medicare.
- 3 months before your birthday month: sign up for Part B if you are not covered by a current employer plan, so coverage starts on time.
- If you keep working: keep proof of your employer group coverage, and note when it ends.
- When work or coverage ends: sign up within the 8-month Special Enrollment Period.
- If you missed everything: use the January 1 to March 31 General Enrollment Period, and expect a penalty.
7. Key takeaways
- Your Initial Enrollment Period is 7 months, from 3 months before to 3 months after your 65th birthday month.
- Signing up for Part B before your birthday month starts coverage the month you turn 65.
- Coverage through a current job, yours or a spouse's, generally allows a Special Enrollment Period ending 8 months after that coverage or job ends.
- The Part B penalty is 10% of the standard premium for each full year you were late, usually for life.
- With the 2026 premium of $202.90, a 2-year delay means paying $243.50 a month instead.