When your doctor’s office tells you “Medicare pays 80%, you’re responsible for the other 20%,” that remaining share is what supplemental insurance is designed to cover. But “supplemental insurance” isn’t one product — it’s three legally distinct categories that work in different ways, and mixing them up can cost you thousands or leave gaps you thought you’d filled.
The short answer
Supplemental insurance adds to your existing health coverage rather than replacing it. For people on Original Medicare (Parts A and B), Medigap covers copays, coinsurance, and deductibles Medicare doesn’t pay. Critical illness and accident insurance work differently — they pay lump sums if you’re diagnosed with a covered condition or hospitalized, regardless of what your primary insurance covers. None of these replace Medicare or function as standalone coverage.
Three types of supplemental insurance — and which one you actually need
The confusion starts with the term itself. “Supplemental health insurance coverage” legally refers to three products regulated under different laws:
Medigap (Medicare Supplement Insurance) is the federally standardized product sold only to people enrolled in Original Medicare. It pays the gaps Original Medicare leaves: the 20% coinsurance for doctor visits, the daily copays for long hospital stays, the Part A deductible. Every Medigap plan with the same letter (Plan G, Plan N, etc.) offers identical benefits no matter which insurance company sells it — only the premium differs. You cannot buy Medigap if you’re enrolled in Medicare Advantage; it’s legally prohibited. Source: CMS Medigap overview
Critical illness insurance pays a lump sum — typically several thousand to $50,000 or more — if you’re diagnosed with a covered illness like cancer, heart attack, or stroke. This money is yours to use however you need: mortgage payments, experimental treatment, travel to a specialist. It works alongside Medicare, Medigap, or Medicare Advantage. State insurance commissioners regulate these products, not federal Medicare law, so benefits and pricing vary widely.
Accident and hospital indemnity insurance pays a fixed amount per day of hospitalization or per accident. If the plan pays $200/day and you’re hospitalized for five days, you get $1,000 regardless of what Medicare or Medigap already covered. These are also state-regulated products and function as income replacement, not gap-filling.
Most people searching for “supplemental insurance” need Medigap. The other two are optional add-ons for people who want cash payouts in specific scenarios.
What Medigap plans actually cover
Medigap plans don’t cover everything Medicare doesn’t. They cover predictable cost-sharing — the deductibles, copays, and coinsurance built into Medicare’s payment structure. Here’s what the most common plans pay:
| What Medicare leaves unpaid | Plan A | Plan G | Plan N |
|---|---|---|---|
| Part A hospital coinsurance (days 61–90) | ✓ | ✓ | ✓ |
| Part A deductible ($1,676 in 2025) | ✗ | ✓ | ✓ |
| Part B coinsurance (20% of doctor visits) | ✗ | ✓ | ✓ up to $20 copay |
| Part B deductible ($240 in 2025) | ✗ | ✗ | ✗ |
| Part B excess charges | ✗ | ✓ | ✗ |
| Foreign travel emergency (80% after $250 deductible) | ✗ | ✓ | ✓ |
Plan G is the most popular Medigap plan sold today because it covers nearly everything except the Part B deductible — a predictable $240 annual cost most enrollees are willing to pay out of pocket. Plan N costs less but requires copays of up to $20 per doctor visit and doesn’t cover Part B excess charges (the extra amount some doctors bill above Medicare’s approved rate). Plan A is the bare-minimum option and leaves you exposed to Part B coinsurance, which can add up fast if you see specialists regularly.
Plans C and F, which used to cover the Part B deductible, were discontinued for new enrollees in 2020. If you enrolled before then, you can keep your plan, but you can’t switch to it now.
What Medigap does NOT cover
Medigap fills Medicare’s gaps — but only the gaps Medicare was designed to have. It does not cover:
- Prescription drugs. You need a separate Medicare Part D plan for medications.
- Dental, vision, or hearing care. Original Medicare doesn’t cover routine dental cleanings, eyeglasses, or hearing aids, so Medigap doesn’t either. You’ll need standalone policies.
- Long-term care or custodial care. If you need help bathing, dressing, or eating at home or in a nursing facility, neither Medicare nor Medigap pays for that.
- Services Medicare doesn’t cover. Cosmetic surgery, acupuncture (in most cases), and experimental treatments aren’t Medicare-approved, so Medigap won’t pay.
The foreign travel benefit is limited: Medigap covers 80% of emergency care outside the U.S. after a $250 deductible, with a $50,000 lifetime maximum. It’s designed for short trips, not expatriate living.
What supplemental insurance actually costs in 2025
Medigap premiums vary more than most people expect. A 65-year-old enrolling in Plan G might pay $140/month in Pennsylvania or $280/month in Florida for the exact same coverage. Three factors drive the difference:
Your state’s rating rules. Most states allow “attained-age” rating, meaning your premium rises as you get older. A handful of states — New York, Pennsylvania, Massachusetts — require “community rating,” where everyone pays the same price regardless of age. California allows “issue-age” rating, where your premium is locked in at the age you enrolled and only increases for inflation and claims experience, not because you turned 70.
Your age at enrollment. Here are typical 2025 premium ranges based on Medicare.gov’s plan comparison tool:
| Plan | Age 65 (issue-age state) | Age 75 (issue-age state) |
|---|---|---|
| Plan A | $90–$150/month | $120–$200/month |
| Plan G | $160–$280/month | $250–$400/month |
| Plan N | $120–$220/month | $180–$320/month |
Which insurance company you choose. Even in the same zip code, Plan G premiums can differ by 30% or more across carriers. Benefits are identical — federal law requires it — but companies price based on their claims experience and how aggressively they want to grow market share.
Expect annual increases. Medigap premiums typically increase annually due to medical inflation and changes in the insured pool. These increases apply to everyone in your plan, not just you, and aren’t based on whether you filed claims.
Supplemental vs comprehensive insurance: the trade-off that actually matters
This is where the confusion peaks. People ask “Is Medigap better than Medicare Advantage?” as if one is universally superior. They’re not comparable that way — they represent two different philosophies about managing healthcare costs.
| Feature | Original Medicare + Medigap (supplemental model) | Medicare Advantage (comprehensive model) |
|---|---|---|
| Monthly premium | Medicare Part B ($174.70 in 2025) + Medigap ($140–$400) = $315–$575/month | $0–$100/month for the plan (Part B premium still required) |
| Provider choice | Any doctor or hospital that accepts Medicare nationwide | Network restrictions; HMO/PPO rules apply |
| Cost predictability | High — most out-of-pocket costs covered by Medigap | Lower — copays/coinsurance per visit; annual out-of-pocket maximum |
| Prescription drug coverage | Requires separate Part D plan | Often included in the plan |
| Referrals for specialists | Not required | Often required (HMO plans) |
| Annual out-of-pocket maximum | None (Medigap covers most gaps) | Yes — typically $3,000–$8,000/year |
The Medigap model front-loads your costs with higher premiums but gives you predictability. If you see specialists frequently, travel between states, or want the security of knowing most bills are covered, Original Medicare plus a Medigap plan delivers that. You pay more every month, but you’re rarely surprised by a bill.
The Medicare Advantage model keeps monthly premiums low but shifts cost-sharing to the point of service. You’ll pay copays every time you visit the doctor, and if you need expensive care — chemotherapy, joint replacement — you’ll hit your out-of-pocket maximum before the plan covers everything. If you’re healthy, use in-network providers, and value lower monthly costs, Medicare Advantage can save you money.
Neither is “supplemental” versus “comprehensive” in the sense of one covering more. They’re structural choices: prepay your healthcare costs (Medigap) or pay as you go (Medicare Advantage). For a deeper comparison of plan structures, see more on hmo vs ppo vs epo: which plan fits your budget and care needs?.
The enrollment deadline you can’t afford to miss
Federal law gives you a six-month Medigap Open Enrollment Period starting the month you turn 65 and enroll in Medicare Part B. During that window, insurance companies must sell you any Medigap plan they offer in your state at standard rates, regardless of your health. They cannot deny you, charge you more, or exclude pre-existing conditions.
Miss that window and the rules change — drastically. After six months:
- In 38 states, insurers can require medical underwriting. If you have diabetes, heart disease, or a history of cancer, they can deny your application or charge you significantly more.
- In 12 states (including California and Oregon), insurers can deny you coverage outright with no obligation to offer an alternative.
- In a handful of states (New York, Connecticut, Massachusetts), you retain guaranteed-issue rights year-round, but these states are the exception.
There is no federal late-enrollment penalty like the one for Medicare Part D, but the practical penalty is worse: permanent rate-loading or outright denial. If you enroll at 65 and pay $180/month for Plan G, but wait until 68 and apply after a health event, you might be quoted $350/month — or nothing at all. Source: California Department of Insurance Medigap guidance
One critical exception: If you’re enrolled in a Medicare Advantage plan and want to switch back to Original Medicare, you have a guaranteed-issue right to buy Medigap Plan A, B, C, F, K, or L within 63 days of leaving the Advantage plan — but only if you’ve been in the plan for less than one year. After that, you’re subject to your state’s underwriting rules.
When supplemental insurance makes sense
You need Medigap if you’re enrolled in Original Medicare and want to avoid unpredictable out-of-pocket costs. Specifically, consider it if you:
- See specialists regularly or have a chronic condition requiring ongoing care
- Travel frequently and want coverage across state lines
- Prefer budgeting a fixed monthly amount rather than guessing what your medical bills will be
- Are taking medications that require frequent doctor monitoring (since Medigap smooths the cost of those visits)
You don’t need Medigap if you’re enrolled in Medicare Advantage — you can’t buy it, and you wouldn’t want to. Medicare Advantage already structures cost-sharing into the plan design.
Critical illness or accident insurance makes sense if you have limited savings and want a cash cushion in case of a major diagnosis or hospitalization. These policies don’t replace Medigap; they supplement it (or supplement Medicare Advantage). Think of them as financial insurance, not health insurance.
FAQ
Can I switch Medigap plans later if I find a cheaper one?
Yes, but only if you pass medical underwriting (in most states). Insurers can require a health questionnaire and deny you or charge more based on your current health. A few states guarantee the right to switch plans annually without underwriting — check your state insurance department’s rules.
Does Medigap cover my spouse?
No. Each person needs their own Medigap policy. If both you and your spouse are on Medicare, you’ll each pay a separate premium.
What happens to my Medigap plan if my insurance company stops selling it?
Your coverage continues — the insurer must renew your policy even if they stop selling new plans. You’re “grandfathered in.” However, the company can still raise your premium annually, and if they exit the market entirely, you’ll need to find a new plan (subject to underwriting in most states).
Is AARP the only place to buy Medigap?
No. AARP-branded plans are underwritten by UnitedHealthcare and are popular, but dozens of insurers sell Medigap. Compare premiums and customer service ratings using Medicare.gov’s plan comparison tool before you buy.
Medigap works best when you enroll during your six-month open enrollment window and choose a plan that matches how much care you actually use. If you’re not sure which plan fits, your state’s SHIP (State Health Insurance Assistance Program) offers free, unbiased counseling — find yours through Medicare.gov or your state insurance department.
For help understanding the out-of-pocket costs Medigap is designed to cover, see more on what is a copay vs coinsurance? the real difference and more on what is a deductible in health insurance? (and why it matters).
This is not insurance or financial advice. Coverage details, premiums, and enrollment rules vary by state and insurer. Consult Medicare.gov, your insurance carrier, or a SHIP counselor for guidance specific to your situation.