Quick answer: what is Medigap?
Medigap (Medicare Supplement insurance) is a private policy that fills the cost-sharing gaps in Original Medicare (Parts A + B). It pays the 20% coinsurance Medicare doesn't, plus the Part A hospital deductible and other out-of-pocket costs depending on which plan letter you choose.
Without Medigap, Original Medicare has no annual out-of-pocket maximum — which is why most beneficiaries pair it with either Medigap or Medicare Advantage.
Coverage is standardized. Plan G from one carrier is identical to Plan G from another. Only price and rate-increase history differ.
Best window to enroll: the 6-month Medigap Open Enrollment Period starting the month you turn 65 AND are enrolled in Part B — guaranteed-issue, no health questions.
What is Medigap, exactly?
Medigap (officially called Medicare Supplement insurance) is a private health insurance policy designed to supplement Original Medicare. It's sold by private insurance carriers — Mutual of Omaha, AARP/UnitedHealthcare, Aetna, Cigna, Anthem Blue Cross Blue Shield, Humana, and others — but the coverage itself is federally standardized.
You only have a Medigap policy if you also have Original Medicare (Parts A and B). Medigap is NOT a replacement for Medicare — it pays AFTER Medicare pays, covering the costs Medicare leaves behind.
You also cannot have Medigap and Medicare Advantage at the same time. They are mutually exclusive: Medicare Advantage replaces Original Medicare with a private plan, while Medigap supplements Original Medicare.
How does Medigap work mechanically?
Here's what happens when you have Original Medicare + Medigap:
- You see a doctor or receive a covered service.
- The provider bills Medicare.
- Medicare pays its share (typically 80% of the Medicare-approved amount for Part B services).
- Medicare automatically sends the remaining 20% (or other applicable cost-sharing) to your Medigap carrier.
- Medigap pays its portion based on your plan letter — for Plan G, that's everything except the Part B annual deductible. For Plan N, it's the same minus office and ER copays.
- You owe little or nothing at the point of service.
There are no networks. Any provider that accepts Medicare must accept your Medigap policy. This means you can see any Medicare-accepting doctor nationwide without referrals or prior authorization — a major distinction from Medicare Advantage.
Want to see what Medigap would cost in your state?
Get A Free Quote →Do you need Medigap? (Or is Medicare Advantage better?)
Original Medicare alone has no out-of-pocket maximum. A single catastrophic hospitalization or chronic illness can result in unlimited cost-sharing. Most beneficiaries pick one of three paths after turning 65:
Original Medicare + Medigap + Part D
- Higher monthly premium ($90-$200+ for Medigap)
- Widest provider network — any Medicare-accepting doctor nationwide
- Most predictable monthly costs (premium + Medigap premium covers nearly everything)
- No referrals, no prior authorization
- Separate Part D drug plan required
- Best for: people who want predictable costs, travel, see specialists, want to keep specific doctors
Medicare Advantage (Part C)
- Lower or $0 monthly premium
- Network restrictions (HMO/PPO)
- Copays for individual services + annual out-of-pocket maximum
- Usually bundles Part D drug coverage
- May include dental, vision, fitness benefits
- Best for: people whose doctors are in-network, want lower premium, don't mind referrals
The 12 standardized Medigap plans (A-N)
Medigap plans are federally standardized by letter. For new enrollees in 2026, three plans dominate:
| Plan | What it covers | Typical premium (2026) |
|---|---|---|
| Plan G | Everything except Part B annual deductible ($257 in 2026). Most popular for new enrollees. | $110 – $200/mo |
| Plan N | Like Plan G but adds $20 office copay + $50 ER copay (waived if admitted). Doesn't cover Part B excess charges (a non-issue in most states). | $90 – $160/mo |
| High-Deductible Plan G | Same coverage as Plan G after a federal annual deductible ($2,870 in 2026). | $40 – $70/mo |
| Plan F | Covers everything including Part B deductible. Closed to anyone Medicare-eligible after January 1, 2020. | Varies (existing enrollees only) |
| Plans A, B, C, D, K, L, M | Older plans with partial coverage. Rarely the best fit for new enrollees compared to G, N, or HD-G. | Varies |
Every Medigap plan of the same letter covers exactly the same things — federally standardized. The only differences between carriers selling the same plan letter are price and rate-increase history. This is why a free comparison across carriers is so valuable: you get identical coverage but can save 30-50% on premium.
When can you enroll in Medigap?
Your one-time 6-month Medigap Open Enrollment Period starts the month you turn 65 AND are enrolled in Part B.
During this 6-month window:
- Every Medigap plan in your state is guaranteed-issue
- Carriers cannot ask health questions
- Carriers cannot decline you or charge more for pre-existing conditions
- No waiting periods for benefits
Outside this window, most states allow medical underwriting — a carrier can decline you, charge more for conditions, or refuse to sell you a Medigap plan at all. Missing the Medigap Open Enrollment window is the single most expensive Medicare mistake new beneficiaries make.
A few states have additional protections: Year-round guaranteed-issue (CT, ME, MA, NY, VT); Birthday Rule for one switch per year (CA, ID, IL, KY, LA, MD, MN, NV, OK, OR); Anniversary Rule (MO).
Want to check if you're inside your Medigap Open Enrollment window?
Get A Free Quote — We'll Check For You →How much does Medigap cost?
Medigap premiums in 2026 vary by state, age at enrollment, ZIP code, gender (in most states), and tobacco use. Typical ranges for new enrollees age 65:
- Plan G: $110 – $200/month — most popular choice
- Plan N: $90 – $160/month — ~$30/mo savings vs Plan G with $20 office / $50 ER copays
- High-Deductible Plan G: $40 – $70/month — lowest premium; federal annual deductible
Premiums increase over time as you age. The carrier with the lowest premium today isn't always the cheapest 5-10 years from now — historical rate stability matters. A good independent agent ranks carriers by both starting premium AND rate-increase history.
Is Medigap worth it?
For beneficiaries who want predictable monthly costs, the freedom to see any Medicare-accepting doctor nationwide without referrals, and the security of capped cost-sharing — yes. The trade-off is higher monthly premium than Medicare Advantage.
People with stable health, doctors already in a Medicare Advantage network, and limited travel often find Medicare Advantage's lower premium worth the network restrictions.
The right answer depends on your doctors, prescriptions, travel patterns, and budget. A licensed independent Medicare agent can model both side-by-side for your specific situation at no cost.
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