At 65 you can enrol in Medicare in the United States. The catch is that "I'll sign up when I need it" does not work — enrolling late adds a penalty to your premium, and for most people it stays for life. We read two pages on Medicare.gov and set them out.
1. The first window is 7 months. It opens 3 months before the month you turn 65 and closes 3 months after.
2. Part B: 10% for each year late. On the 2026 standard premium of $202.90, 2 years late adds 20%, making $243.50 (the Medicare.gov example).
3. Part D: 1% for each month late. That is 12% a year. The penalty is not a one-off fine; it rides on the premium every month.
Three windows for signing up
| Period | When | Coverage starts |
|---|---|---|
| Initial Enrollment Period | 7 months — from 3 months before the month you turn 65 to 3 months after | The month you turn 65 if you sign up before it; the next month if you sign up in that month or the 3 months after |
| General Enrollment Period | 1 January to 31 March each year | The month after you sign up |
| Special Enrollment Period | With job-based group cover: 8 months after that cover or the employment ends, whichever comes first | Generally the month after you sign up |
The first "coverage starts" row is for Part B and premium Part A. Premium-free Part A starts the month you turn 65, or the month before if your birthday is on the 1st. Special Enrollment Periods also exist for losing Medicaid, disasters, release from incarceration and other situations, each with its own length — only the job-based one is carried over here.
Our example. Turning 65 in June gives an Initial Enrollment Period from March to September. Miss it with no special situation and you wait for the General Enrollment Period in January to March of the next year, with the penalty building in between.
The penalties — three, each separate
Medicare.gov says the penalties are added to the monthly premium, are not a one-time late fee, and are usually charged for as long as you have that coverage — a lifetime for most people.
| Part | How it is added | For how long |
|---|---|---|
| Part A (hospital) | If you have to buy Part A and do not when first eligible, the monthly premium may rise 10% | Twice the number of years you did not sign up — 2 years late means 4 years |
| Part B (medical) | 10% for each year you could have signed up but did not | As long as you have Part B |
| Part D (drugs) | 1% for each month (12% a year), applied to the national base premium | As long as you have Medicare drug coverage, across plan changes |
The Part A penalty, as the page puts it, concerns those who have to buy Part A — who gets it premium-free was not read on these pages. The Part D penalty applies when you go 63 days or more without creditable drug coverage.
In numbers — 2026
| Case | Working | Monthly premium |
|---|---|---|
| Part B, on time | 2026 standard premium | $202.90 |
| Part B, 2 years late (Medicare.gov example) | 202.90 + 40.58 (20%) = 243.48 → rounded to the nearest $0.10 | $243.50 |
| Part B, 3 years late (our arithmetic) | 202.90 + 60.87 (30%) = 263.77 | $263.80 |
| Part D, 14 months late (Medicare.gov example) | 38.99 × 14% | Plan premium + $5.50 |
The 3-year row follows the Medicare.gov method (10% a year, rounded to the nearest $0.10) and is our arithmetic. When the standard premium changes from year to year, the penalty in dollars changes with it — the percentage is fixed, not the amount (our reading). The page notes that Part B premiums can be higher at higher incomes; those brackets are not covered here.
When no penalty applies
- If you qualify for a Special Enrollment Period you generally pay no Part B penalty — working past 65 with job-based group cover is the typical case.
- If you are in a Medicare Savings Program there is no Part B penalty.
- For Part D, having creditable drug coverage or qualifying for Extra Help avoids the penalty.
Which cover counts as job-based group cover (whether COBRA or retiree insurance does, for instance) was not checked on these two pages. Confirm it separately when you retire — COBRA periods are in US health insurance terms.
Checklist
- ☐ Marked the month you turn 65 and the 7-month Initial Enrollment Period
- ☐ If job-based cover continues past 65, counted 8 months from the day it ends
- ☐ If delaying Part D, kept proof of creditable drug coverage
- ☐ No gap of more than 63 days without drug coverage
Questions that remain
Am I enrolled automatically if I draw Social Security?
These two pages do not cover automatic enrolment, so we did not confirm it. Claiming ages are in US Social Security.
What if I plan to move back to Korea?
We did not read the enrolment and penalty rules for people living abroad, nor whether care outside the US is covered — ask the SSA before deciding to delay.
How does it relate to an HSA?
HSA rules are in HSA vs FSA. The link between Medicare enrolment and HSA contributions was not read this time.
Sources
- Medicare.gov, Avoid late enrollment penalties — original (checked 7 October 2026). Part A 10% and twice the years; Part B 10% a year; 2026 figures $202.90, $40.58, $243.48, $243.50; Part D 1% a month, $38.99, $5.50 for 14 months; 63 days.
- Medicare.gov, When does Medicare coverage start? — original. The 7-month Initial Enrollment Period, the General Enrollment Period of 1 January to 31 March, the 8-month job-based Special Enrollment Period, and coverage start dates.
- Not read. Income-related Part B premiums, automatic enrolment, what counts as job-based cover, rules for residents abroad, Medicare Advantage and Medigap.
- Our arithmetic and reading. The June birthday example, $263.80 at 3 years late.
Where to check further
- Medicare.gov and the Social Security Administration — signing up and confirming your own enrolment period.
- The wider health insurance frame — US health insurance terms.
Written on 7 October 2026. The rules and 2026 amounts are set out from Medicare.gov; the examples and glosses are ours. This is not advice on your own situation.
