Most people don't think seriously about Medicare until they're 64 years old and suddenly realize enrollment deadlines are approaching. That's too late for good planning. The decisions you make around Medicare — when you enroll, which parts you choose, whether you add supplemental coverage — have lasting financial consequences that are difficult and sometimes impossible to reverse.
Here is what you need to know before you reach 65.
The Four Parts of Medicare
Part A — Hospital Insurance
Covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people pay no premium for Part A if they or their spouse worked at least 10 years and paid Medicare taxes. Comes with a deductible per benefit period ($1,676 in 2025).
Part B — Medical Insurance
Covers doctor visits, outpatient services, preventive care, and durable medical equipment. Requires a monthly premium ($185/month standard in 2025, higher for higher incomes). Has an annual deductible ($257 in 2025) and 20% coinsurance after that.
Part C — Medicare Advantage
An alternative to Original Medicare offered by private insurers. Bundles Parts A and B (and usually Part D) into a single plan, often with additional benefits like dental and vision. Uses network restrictions like HMOs and PPOs. May have lower premiums but higher out-of-pocket costs when care is needed.
Part D — Prescription Drug Coverage
Covers prescription medications through private insurance plans. If you don't enroll when first eligible and don't have creditable drug coverage, you pay a permanent late enrollment penalty for every month you delay.
When to Enroll — and the Penalties for Missing It
Medicare has strict enrollment windows, and missing them triggers permanent penalties that last as long as you have Medicare.
Initial Enrollment Period (IEP): A 7-month window — 3 months before your 65th birthday, the month of, and 3 months after. This is your primary enrollment window.
Part B late enrollment penalty: If you don't enroll in Part B during your IEP and don't have qualifying employer coverage, you pay a permanent 10% penalty on your Part B premium for every 12-month period you were eligible but not enrolled. Miss it by two years and your Part B premium is permanently 20% higher — for life.
Part D late enrollment penalty: 1% of the national base beneficiary premium for every month you went without creditable drug coverage. Also permanent.
Still Working at 65? Read This Carefully.
If you're still employed at 65 and covered by employer health insurance, you may be able to delay Medicare enrollment without penalty — but the rules depend on the size of your employer. If your employer has 20 or more employees, your group plan is the primary payer and you can delay Medicare. If your employer has fewer than 20 employees, Medicare becomes primary at 65 and you should enroll to avoid gaps and penalties. Verify your situation with your HR department or a Medicare counselor before your 65th birthday.
Original Medicare vs. Medicare Advantage
This is the most consequential Medicare decision most people make — and it's one that can be difficult to reverse.
Original Medicare (Parts A + B): Accepted by virtually every doctor and hospital in the U.S. No network restrictions. You pay 20% of covered costs with no out-of-pocket maximum (which is why most people add a Medigap supplement). Flexibility to see any Medicare-accepting provider anywhere in the country.
Medicare Advantage (Part C): Offered through private insurers. Lower or zero monthly premiums in many plans. Often includes dental, vision, and hearing benefits that Original Medicare doesn't cover. However: network restrictions mean you may not be able to see your preferred doctors, prior authorization requirements can create delays, and out-of-pocket maximums can reach $8,850 or more. Coverage quality varies significantly by plan and geography.
| Feature | Original Medicare | Medicare Advantage |
|---|---|---|
| Provider access | Any Medicare provider nationwide | Network restrictions (HMO/PPO) |
| Monthly premium | Part B premium only ($185+) | Often lower or $0 (after Part B) |
| Out-of-pocket maximum | No cap (need Medigap) | Capped (up to $8,850 in-network) |
| Prescription drugs | Requires separate Part D plan | Usually bundled |
| Dental / Vision / Hearing | Not covered | Often included |
| Prior authorization | Rarely required | Common |
| Travel / out-of-area care | Covered anywhere in US | Limited outside network area |
Medigap: Filling the Gaps in Original Medicare
Original Medicare covers about 80% of costs after deductibles. The remaining 20% — with no out-of-pocket cap — can be substantial in a serious illness. Medigap (Medicare Supplement) plans are private insurance policies that cover some or all of those remaining costs.
The best time to buy a Medigap policy is during your 6-month Medigap Open Enrollment Period, which starts the month you turn 65 and enroll in Part B. During this window, insurers must sell you any Medigap policy at standard rates regardless of health conditions. After this window, insurers can use medical underwriting — meaning pre-existing conditions can result in higher premiums or denial of coverage entirely.
IRMAA: How Your Income Affects Your Premium
Higher-income Medicare beneficiaries pay more for Parts B and D through Income-Related Monthly Adjustment Amounts (IRMAA). The surcharges are based on your income from two years prior — so your 2025 Medicare premium is based on your 2023 tax return.
| Individual Income (2023) | Monthly Part B Premium (2025) |
|---|---|
| $106,000 or less | $185.00 |
| $106,001 – $133,000 | $259.00 |
| $133,001 – $167,000 | $370.00 |
| $167,001 – $200,000 | $480.90 |
| Above $200,000 | $591.90 |
This is a significant retirement planning consideration. A large Roth conversion or asset sale in a single year can push you into a higher IRMAA bracket two years later. Thoughtful income management in retirement can help you avoid these surcharges.
The Bottom Line
Medicare is more complex than most people expect, and the decisions you make at 65 — particularly around whether to choose Original Medicare or Medicare Advantage, and whether to buy a Medigap policy — can affect your healthcare access and costs for the rest of your life. The time to understand these choices is before you're in the enrollment window, not during it. Building a realistic healthcare cost estimate into your retirement plan — including potential IRMAA surcharges — is essential to avoiding an expensive surprise.