🎯 In 30 seconds: Medicare starts at 65 and has firm sign-up windows. Miss them without other qualifying coverage and the penalties can last as long as you have the coverage. Learn the parts, mark your Initial Enrollment Period, find out whether your employer’s plan pays first, and use the free plan finder and a free SHIP counselor.
The parts in one table
| Part | Covers | 2026 cost basics |
|---|---|---|
| A | Hospital stays, skilled nursing, hospice | Usually no premium after about 10 years of Medicare taxes; $1,736 deductible per benefit period |
| B | Doctors, outpatient care, tests, equipment | $202.90 a month standard premium (more at higher incomes); $283 yearly deductible |
| C (Medicare Advantage) | Private plans that replace A and B, usually with drug coverage | Varies by plan; you still pay the Part B premium |
| D | Prescription drugs | Varies by plan |
| Medigap | Private supplement that pays some costs Original Medicare leaves | Varies; works only with Original Medicare |
The core choice: Original Medicare (A and B) plus a Part D plan and possibly Medigap, or a Medicare Advantage plan. It is illegal to sell you a Medigap policy while you are in Medicare Advantage.
Signing up around 65
- Your Initial Enrollment Period lasts 7 months: 3 months before the month you turn 65, that month, and 3 months after.
- Coverage always starts on the first of a month. Signing up in the months before your birthday month avoids a gap.
- Each year, Open Enrollment runs October 15 to December 7, when you can switch between Original Medicare and Medicare Advantage or change drug plans; changes start January 1.
Still working at 65
Who pays first depends on the size of your (or your spouse’s) current employer:
| Employer has 20 or more employees | The employer plan pays first; many people delay Part B without penalty |
| Fewer than 20 employees | Medicare pays first; delaying Part B can leave large bills unpaid |
When the job or the coverage ends, a Special Enrollment Period lets you sign up for Part B without penalty within 8 months. COBRA and retiree coverage do not count as current-employment coverage, so the 8-month clock runs even while you are on COBRA. Ask the employer’s benefits office in writing how its plan works with Medicare.
Late penalties, worked through
- Part B: 10% added to the premium for each full 12 months you could have had Part B and did not, generally for as long as you have Part B.
- Part D: 1% of the national base beneficiary premium ($38.99 in 2026) for each month you went without creditable drug coverage after your Initial Enrollment Period, once the gap is 63 days or more.
| Part B delayed 2 full years without a Special Enrollment Period | 20% penalty: $243.50 a month instead of $202.90 in 2026 |
| Extra cost over a year | about $487, and it repeats every year |
| Part D: 14 months without creditable coverage | 14% × $38.99 ≈ $5.46 a month on top of the plan premium |
Medigap: the one-time window
Your Medigap Open Enrollment Period is the 6 months starting the first month you are 65 or older and enrolled in Part B. During it, insurers must sell you any Medigap policy they offer without charging more for health conditions. Outside it there is no general federal guarantee, so switching from Medicare Advantage back to Original Medicare later may leave you unable to buy Medigap at a normal price.
Choosing a plan and free help
- List your doctors, hospitals and prescriptions with doses.
- Use the Medicare.gov Plan Finder to compare drug plans and Medicare Advantage plans on total yearly cost, not just the premium.
- Book a free, unbiased session with your State Health Insurance Assistance Program (SHIP). SHIP counselors do not sell insurance.
- Repeat the check every fall in Open Enrollment, because plan drug lists and networks change yearly.
For how Medicare fits the rest of retirement, see the roadmap by decade.