Original Medicare pays most of your medical bills, but not all of them. It leaves you on the hook for deductibles, copayments, and a 20% coinsurance on Part B services that has no annual out-of-pocket maximum. One long hospital stay or an aggressive course of cancer treatment can turn that open-ended 20% into a five-figure bill. A Medicare Supplement policy — almost everyone calls it Medigap — is the private insurance designed to close those gaps.

Medigap is sold by private insurers, but the plans themselves are standardized by federal law. That is the part most people get wrong. A Plan G from one insurer covers italic exactly the same benefits as a Plan G from another. Only the price and the customer service differ. Once you understand the lettered plans, shopping becomes a math problem, not a guessing game.

How Medigap works alongside Original Medicare

Medigap only works with Original Medicare — Parts A and B run by the federal government. It does not work with Medicare Advantage, the private alternative that bundles everything into one plan. You cannot legally hold both a Medigap policy and a Medicare Advantage plan at the same time, and that single rule shapes the entire decision new retirees face at 65.

Here is the sequence. Medicare pays its share of an approved service first. Then your Medigap policy automatically pays its share of what is left — the coinsurance, the copay, or the deductible the plan covers. You rarely see a bill. There are no networks and no referrals: any provider in the country who accepts Medicare accepts your Medigap policy, because the supplement simply follows Medicare’s payment.

That nationwide freedom, with predictable costs, is the reason Medigap still exists in an era when Medicare Advantage markets itself aggressively on $0 premiums.

What Medigap covers — and the gaps that matter in 2026

The gaps Medigap is built to fill are real dollars in 2026. The Centers for Medicare & Medicaid Services set the Part A inpatient hospital deductible at $1,736 per benefit period for 2026, up from $1,676 in 2025. After 60 days in the hospital, you owe $434 a day; lifetime reserve days run $868 a day. On the Part B side, the standard premium is $202.90 a month and the annual deductible is $283, after which the open-ended 20% coinsurance begins.

A comprehensive Medigap plan absorbs most or all of those amounts. The most generous letters cover the Part A deductible, the Part A and skilled nursing coinsurance, the Part B 20% coinsurance, the three pints of blood, hospice cost-sharing, and a slice of foreign-travel emergency care. What separates the two plans almost everyone buys today comes down to a handful of line items.

Plan G: the default choice for new enrollees

Plan G is now the most popular Medigap policy for people aging into Medicare. It covers everything the old, richer Plan F covered with one exception: it does not pay the $283 Part B deductible. You pay that yourself, once a year, and then Plan G covers the rest — including the 20% Part B coinsurance that has no cap under Original Medicare.

That structure is why advisors steer most healthy 65-year-olds toward Plan G. You take on a small, fixed, predictable cost ($283 a year) in exchange for near-total protection against the catastrophic, unpredictable cost (an unlimited 20% on a major illness). Plan F, which italic did cover the Part B deductible, is closed to anyone who became eligible for Medicare on or after January 1, 2020. If you were eligible before that date you can still buy Plan F, but for new retirees the realistic top-tier choice is Plan G.

Plan N: a lower premium in exchange for small copays

Plan N is the value option, and the second most common pick. It covers the same big-ticket items as Plan G — the Part A deductible, the Part A and Part B coinsurance — but asks you to absorb three things Plan G handles for you:

  • a copay of up to $20 for some office visits and up to $50 for an emergency room visit that does not lead to admission;
  • the $283 Part B deductible, just like Plan G;
  • Part B excess charges — the extra amount (up to 15% above the Medicare-approved rate) that a provider who does not accept “assignment” is allowed to bill.

In exchange, Plan N typically carries a meaningfully lower monthly premium than Plan G. For someone who rarely sees specialists, almost never lands in the ER, and lives in a state where excess charges are banned or rare, Plan N can save real money over a retirement without giving up the catastrophic protection that matters most.

High-Deductible Plan G: the lowest premium, the biggest bet

There is a third option worth knowing. High-Deductible Plan G carries the same benefits as standard Plan G but does not start paying until you have spent $2,950 out of pocket in 2026. In return, the monthly premium is dramatically lower — often a fraction of standard Plan G. It suits a healthy retiree who wants Medigap mainly as catastrophic insurance and is comfortable self-funding routine costs up to the deductible. It is a worse deal for anyone who expects heavy, steady medical use.

What Medigap costs in 2026 — and why the same plan has different prices

Because benefits are standardized, premiums are where insurers compete. Industry surveys generally put standard Plan G in the range of roughly $140 to $300 a month for a 65-year-old, and Plan N somewhat lower, but your actual quote depends on three things: your age, your ZIP code, and how the insurer prices the policy.

That third factor is the one buyers overlook. Medigap policies are priced one of three ways:

  • Community-rated: everyone pays the same premium regardless of age. It looks expensive at 65 but does not rise simply because you get older.
  • Issue-age-rated: the premium is locked to your age when you buy. Buy younger, lock in lower.
  • Attained-age-rated: the premium starts low at 65 and climbs every year as you age. It is the cheapest on day one and frequently the most expensive a decade later.

Two policies with identical benefits can diverge by hundreds of dollars a year over time purely because of pricing method. Since a Medigap premium becomes a italic permanent line in your budget — a fixed cost you carry for as long as you hold the policy — it is worth weighing alongside the rest of your retirement income plan, including when you choose to claim Social Security.

The one window that sets your price for life

The single most important rule in Medigap is the timing of your purchase. Your Medigap Open Enrollment Period is a one-time, six-month window that starts the first month you are both age 65 italic and enrolled in Part B. During those six months you have a guaranteed issue right: an insurer must sell you any Medigap policy it offers, at its best available price, and cannot turn you down or charge you more because of your health history.

Miss that window and, in most states, the protection evaporates. Outside it, insurers can medically underwrite you — review your conditions, raise your premium, or deny coverage outright. Someone who started on Medicare Advantage at 65 and later tries to switch to Original Medicare with a Medigap policy can find that the supplement is now unaffordable or unavailable. A few states (Connecticut, New York, and others) require year-round guaranteed issue, but you should never assume yours does. Buy during the open window, or you may not get a second chance at a good price.

What Medigap does not do

Two limits matter. First, Medigap does italic not cover prescription drugs. You need a separate Part D plan, which in 2026 caps your out-of-pocket drug spending at $2,100 for the year. Second, a Medigap policy covers only one person — spouses each buy their own. And because it pairs only with Original Medicare, choosing Medigap is also a choice italic against Medicare Advantage, with all the network-freedom trade-offs that decision carries.

The bottom line

For most people retiring on Original Medicare, the real choice is narrow: Plan G for near-total protection at a higher premium, Plan N for a lower premium with small, manageable copays, or High-Deductible Plan G for the lowest premium and the largest upfront exposure. Decide before your six-month window closes, compare at least three insurers on the italic same lettered plan, and check whether each quote is attained-age or issue-age rated. Same benefits, very different bills over twenty years — and the timing of when you buy is the one part you cannot redo.

Sources

  • Centers for Medicare & Medicaid Services, “2026 Medicare Parts A & B Premiums and Deductibles,” November 14, 2025.
  • Centers for Medicare & Medicaid Services, “Final CY 2026 Part D Redesign Program Instructions,” April 7, 2025.
  • Medicare.gov, “Compare Medigap plan benefits” and “When can I buy Medigap?”

italic This article is for general information and is not individualized insurance or financial advice. Plan availability, pricing, and state rules vary; confirm current details on Medicare.gov before enrolling.