Medicare enrollment has hard deadlines and penalties that last for life. Your first window, the Initial Enrollment Period, runs seven months: three months before the month you turn 65, that month, and three months after. If you miss it without job-based coverage, Part B costs 10% more for each full year you waited, permanently. In 2026 the standard Part B premium is $202.90 a month, and it’s higher if your income two years earlier was above $109,000 for a single filer or $218,000 on a joint return.
The money decisions are less about which card to carry and more about timing, income and the one window that sets your choices for years.
The windows that matter
| Window | When | What it’s for |
|---|---|---|
| Initial Enrollment Period | 3 months before to 3 months after the month you turn 65 | First chance to sign up for Parts A, B and D |
| Special Enrollment Period | Up to 8 months after job-based coverage or the job ends, whichever is first | Signing up late without a penalty, if you were covered through work |
| General Enrollment Period | January 1 to March 31 | Signing up late, with any penalty |
| Open Enrollment | October 15 to December 7 | Changing between Original Medicare and Medicare Advantage, or drug plans, for January 1 |
| Medicare Advantage Open Enrollment | January 1 to March 31 | Leaving a Medicare Advantage plan for another, or for Original Medicare |
| Medigap Open Enrollment | 6 months from the first month you have Part B and are 65 or older | Buying any Medigap policy without health questions |
Coverage always starts on the first of a month. Sign up before your birthday month and Part B starts the month you turn 65; sign up later in the window and it starts the month after.
Penalties, and how to avoid them
- Part B: 10% of the standard premium for each full 12 months you could have enrolled and didn’t, for as long as you have Part B. Two years late in 2026 means $243.50 a month instead of $202.90.
- Part D: 1% of the national base premium ($38.99 in 2026) for each month without creditable drug coverage, added for as long as you have drug coverage.
- Part A: Most people pay no premium. Those who must buy it, with fewer than 40 quarters of work, pay up to $565 a month in 2026, and 10% more for twice the number of years they delayed.
The exception is job-based coverage from current work, yours or your spouse’s. Then you can usually wait. Two rules trip people up here. COBRA doesn’t count as job-based coverage, and it doesn’t extend the eight-month window. And whether Medicare or your employer’s plan pays first can depend on the employer, so get the plan’s answer in writing before you skip Part B.
Health savings accounts and the six-month lookback
You can’t contribute to a health savings account once you’re enrolled in Medicare. If you sign up for premium-free Part A after 65, coverage starts up to six months back, though never before the month you turned 65. Contributions for those months become excess contributions. Medicare’s advice is to stop HSA contributions, yours and your employer’s, six months before you sign up. Money already in the HSA can still pay Medicare premiums and other medical costs tax-free.
The income lines that set your premium
Part B and Part D premiums rise with income through an extra charge called IRMAA, the income-related monthly adjustment amount. Social Security uses your modified adjusted gross income from two years before, so 2026 premiums are based on 2024 returns.
Part D adds $14.50 to $91.00 a month on top of your plan’s premium across the same brackets. For a married couple both on Medicare, crossing the first joint line by a dollar costs $81.20 a month each in Part B alone, or $1,948.80 a year (2026 amounts, worked out from the CMS figures).
Two planning points follow:
- The years from 63 matter. A large Roth conversion, a home sale or a big capital gain at 63 shows up in your premiums at 65. Plan big income years with the brackets in view.
- Some drops in income can be counted early. If you stop working, cut your hours, marry, divorce, lose a spouse, or lose a pension, you can ask Social Security to use your newer, lower income. A one-time gain from selling a house or converting to a Roth isn’t on that list.
Original Medicare with Medigap, or Medicare Advantage
This is the choice with the longest tail. Original Medicare with a Medigap policy and a Part D plan lets you see any provider that takes Medicare, with predictable costs. A Medicare Advantage plan bundles coverage, often with a lower premium, but uses networks and its own cost sharing.
The money point is the Medigap window. For six months from the first month you have Part B at 65 or older, an insurer can’t refuse to sell you any Medigap policy it offers or charge more for your health. After that, you may not be able to buy one, or it may cost more. Someone who starts in Medicare Advantage and wants to switch at 75, after a diagnosis, may find the door closed. Medigap Plans K and L cap your yearly out-of-pocket costs, at $8,000 and $4,000 in 2026.
Common mistakes
- Assuming COBRA or retiree coverage lets you delay Part B. Neither counts as coverage from current work.
- Contributing to an HSA right up to enrollment. The six-month lookback turns those contributions into excess ones.
- Doing a big Roth conversion at 63 or 64 without checking the brackets.
- Choosing Medicare Advantage for the low premium without considering the Medigap window.
- Not appealing a premium after retiring. Stopping work is a recognized reason to ask for a lower charge.
Questions to ask a planner
| Ask | A good answer includes |
|---|---|
| Do I need Part B at 65, given my coverage? | Your employer’s size and plan rules, checked in writing |
| When should I stop HSA contributions? | A date six months before you’ll sign up |
| How do my Roth conversions affect my premiums? | Each year’s income against the brackets, two years ahead |
| Should I ask for a lower premium after retiring? | Whether your income drop qualifies |
| Medigap or Medicare Advantage for me? | Your doctors, travel, health and budget, not a commission |
When a fee-only advisor is worth it, and what it costs
Picking a specific plan is something your State Health Insurance Assistance Program (SHIP) can help with for free, and Medicare points people there. Where a planner earns their fee is everything around it: the timing of retirement and enrollment, the income years from 63 on, the HSA cutoff, and how Medicare fits the tax plan. An insurance agent who sells Medicare plans is paid when you buy one. A fee-only planner isn’t.
A one-time plan at a median $2,000 covers this well if you’re also setting your retirement income. Hourly planners charge a median $300 to answer a narrower question, such as whether you can delay Part B. Ongoing planning runs a median $4,500 a year (middle half $2,400 to $7,200).
How to find one
Look at advisors for retirees and pre-retirees, the retirement planning specialty, or tax planning if conversions are part of the plan. The retiree audience page gathers related guides. If you’re still deciding when to stop work, read when you can retire first.