What supplemental insurance does, and why you might need it

Original Medicare covers a lot, but not everything. When you go to the hospital or see a doctor, you pay a deductible before Medicare starts paying, and then you pay a percentage of the cost — usually 20 percent — after that. For prescription drugs, you pay out of pocket until you hit a spending threshold, then you pay again once you spend enough to enter the "donut hole." Supplemental insurance — also called Medigap — fills those gaps by paying some or all of the costs Medicare leaves you responsible for.

Without supplemental coverage, a single hospital stay or a course of expensive treatment can cost thousands of dollars. Supplemental insurance does not replace Medicare; it works alongside it. Medicare pays first, then your supplemental plan pays what Medicare does not cover, up to the limits of your plan.

You are not required to buy supplemental insurance. Some people choose Medicare Advantage (Part C) instead, which is a different type of coverage run by private insurance companies. Others stay on Original Medicare alone and accept the out-of-pocket costs. But if you want predictable medical expenses and protection against very high bills, supplemental insurance is the most straightforward option.

Key Takeaways

  • Supplemental insurance pays the deductibles, coinsurance, and copayments that Original Medicare does not cover.
  • You can only buy supplemental insurance during your initial enrollment period (the six months starting when you turn 65 and enroll in Medicare Part B) or during the annual open enrollment period, with limited exceptions.
  • Insurance companies cannot deny you or charge you more based on your health if you buy during your initial enrollment period, but that protection ends after that window closes.
  • There are ten standardized supplemental plans (labeled A through N), and the coverage each one offers is the same no matter which company sells it — only the price differs.
  • Supplemental insurance does not cover prescription drugs; you need a separate Part D plan for that.

The ten standardized plans and what they cover

All supplemental plans are standardized by federal law. Plan A covers one set of costs, Plan B covers a different set, and so on through Plan N. The coverage is identical regardless of which insurance company sells it — a Plan G from Company X covers exactly the same things as a Plan G from Company Y. The only difference is price.

The most popular plans are G, N, and F (though Plan F is no longer sold to people newly may be able to access for Medicare). Plan G covers your Part B deductible, coinsurance, copayments for hospital and doctor visits, and some costs for skilled nursing facilities. Plan N is less expensive but requires you to pay a copayment at the doctor's office and a higher copayment at urgent care. Plan A is the least expensive but covers fewer costs.

You can view a comparison chart of all ten plans on the Medicare website. Each plan shows exactly what it covers and what you still pay out of pocket. Because the plans are standardized, you can compare prices across different insurance companies for the same plan letter without worrying that one company's Plan G is weaker than another's.

When you can buy supplemental insurance and what happens if you miss the window

The best time to buy supplemental insurance is during your initial enrollment period, which runs for six months starting the month you turn 65 and enroll in Medicare Part B. During this window, insurance companies cannot refuse to sell you a plan or charge you more because of any health condition you have — a protection called may provide issue.

If you miss this window, you can still buy supplemental insurance during the annual open enrollment period, which runs from October 15 to December 7 each year. Coverage begins January 1. However, outside your initial enrollment period, insurance companies can deny you coverage or charge you higher premiums based on your health history. Some states have additional protections that extend may provide issue rights, but these vary.

A few exceptions exist: if you were covered by a group health plan through an employer and that coverage ended, you may have a special enrollment period. If you switched from Medicare Advantage back to Original Medicare, you also have a limited window to buy supplemental insurance without medical underwriting. The rules are complex, so contact your state's health insurance counselor (through the State Health Insurance information Program, or SHIP) if you think you may have access to for an exception.

How supplemental insurance premiums work and what affects the cost

Supplemental insurance premiums vary widely depending on the plan you choose, the insurance company, and where you live. The same Plan G might cost $100 a month with one company and $180 with another. Prices also differ by state and sometimes by county.

Insurance companies use three main methods to set premiums. Community-rated plans charge everyone the same price regardless of age. Issue-age-rated plans base the price on how old you were when you bought the plan — if you buy at 65, you pay one rate for life (though the company can raise rates for everyone in your plan). Attained-age-rated plans increase your premium as you get older, so your cost goes up each year on your birthday. Attained-age plans are usually the cheapest to start but the most expensive over time.

You can shop for supplemental insurance by contacting insurance companies directly, using the Medicare Plan Finder on Medicare.gov, or calling your state's SHIP program. SHIP counselors are free and can help you compare plans and prices in your area.

Supplemental insurance versus Medicare Advantage: which path to choose

Medicare Advantage (Part C) is an alternative to Original Medicare plus supplemental insurance. With Advantage, a private insurance company provides your hospital and doctor coverage instead of the federal government. Advantage plans often include prescription drug coverage and extras like dental or vision, and they usually have lower or no premiums.

The trade-off is that Advantage plans typically have networks — you must use doctors and hospitals in the plan's network, or pay more. They also have annual out-of-pocket spending limits, which means your costs are capped, but you may pay more per visit than you would with Original Medicare plus supplemental insurance. Advantage plans can change their benefits and networks each year, so what you have today may not be the same next year.

Supplemental insurance offers more flexibility: you can see any doctor who accepts Medicare, and your coverage stays the same year to year (though premiums may increase). The downside is that you pay a separate premium for supplemental insurance on top of your Medicare Part B premium, and you need a separate Part D plan for prescriptions.

Neither choice is universally better — it depends on your health, your doctors, your budget, and how much predictability matters to you. If you have chronic conditions and see specialists, supplemental insurance may cost less overall. If you are healthy and do not mind network restrictions, Advantage may save you money upfront.

What supplemental insurance does not cover

Supplemental insurance fills gaps in Original Medicare, but it does not cover everything. It does not pay for prescription drugs — you need a separate Part D plan for that, and you can enroll in Part D at the same time you enroll in Medicare. Supplemental insurance also does not cover routine dental, vision, or hearing care, though some Medicare Advantage plans do.

Supplemental insurance does not cover care outside the United States, except in limited circumstances (like emergency care in a country you are traveling through). It also does not cover long-term care, assisted living, or custodial care — the kind of help you need if you cannot bathe or dress yourself. For that protection, you would need a separate long-term care insurance policy, which is expensive and must be bought before you turn 65 in most cases.

Finally, supplemental insurance does not cover costs related to services Medicare itself does not cover. If Medicare does not pay for a treatment, your supplemental plan will not either. For example, if Medicare denies a procedure as not medically necessary, your supplemental plan will not override that decision.

How to enroll in supplemental insurance

Start by contacting insurance companies directly or using the Medicare Plan Finder on Medicare.gov to see which plans are available in your area and what they cost. You can also call your state's SHIP program — the counselor will help you compare plans and answer questions at no cost.

Once you have chosen a plan and company, you contact the insurance company to enroll. You will need your Medicare card and information about any current health coverage. If you are enrolling during your initial enrollment period (within six months of turning 65 and enrolling in Part B), you have may provide issue rights and the company cannot deny you or charge more based on health.

Coverage typically begins the first day of the month after the insurance company receives and approves your enrollment form. Some companies process applications faster than others, so submit your form as soon as you have made your decision. Keep a copy of your enrollment confirmation for your records.

Frequently Asked Questions

Can I switch supplemental plans or insurance companies after I enroll?

Yes, you can switch during the annual open enrollment period (October 15 to December 7) or during your state's annual open enrollment window for supplemental insurance, which may differ from the federal dates. If you switch outside your initial enrollment period, the new company can medically underwrite you and charge higher premiums based on your health. Some states allow switching without underwriting once per year.

Do I need supplemental insurance if I have a Medicare Advantage plan?

No. Supplemental insurance is designed to work with Original Medicare. If you have Medicare Advantage, you cannot buy supplemental insurance — Advantage already includes hospital and doctor coverage. If you switch from Advantage to Original Medicare, you can then buy supplemental insurance, but only during certain windows.

What happens to my supplemental insurance if I move to a different state?

Your coverage continues, but you may want to shop for a new plan in your new state because prices vary by location. You can switch plans during the annual open enrollment period. If you move, contact your insurance company to update your address and confirm your coverage.

Does supplemental insurance cover the Part B deductible?

It depends on the plan. Plan A, Plan B, Plan D, Plan G, Plan M, and Plan N all cover the Part B deductible. Plans C, F, K, and L do not. Check your plan letter to see whether your deductible is covered.

Can I buy supplemental insurance if I have a pre-existing condition?

Yes, if you buy during your initial enrollment period — insurance companies cannot deny you or charge more based on health during that six-month window. If you buy outside that window, companies can medically underwrite you and may deny coverage or charge higher premiums. Some states offer additional protections for people with certain conditions.