Illinois Medigap & the Birthday Rule Explained (2026)

Illinois has a Medicare Supplement (Medigap) "birthday rule," but it is narrower than the one you may have read about in other states. In Illinois, only policyholders who are at least 65 but no more than 75 years old get a 45-day window each year, starting on their birthday, to switch without medical underwriting to an equal-or-lesser Medigap plan from the same insurer (or an affiliate authorized in Illinois). This guide explains exactly how the Illinois birthday rule works, who qualifies, how the standardized A-through-N plans fit together, which plans are closed to newer enrollees, and who regulates Medigap in the state.1

How Medigap works in Illinois

A Medigap policy is private insurance that pays the deductibles and coinsurance Original Medicare leaves to you. Medigap (Medicare Supplement Insurance) works only alongside Original Medicare, not with a Medicare Advantage plan, and each policy covers one person. A married couple who both want coverage need two separate policies.2

Illinois uses the federal standardized framework. Medigap is sold as lettered plans, A through N, and the benefits inside each letter are fixed by federal rule. A Plan G from one Illinois insurer covers exactly what a Plan G from another covers. Insurers compete on price, service, and rate stability, not on what the plan pays. That makes the plan letter your first decision and the insurer your second.2

The gaps Medigap closes are real. In 2026, after the Part B deductible of $283, Original Medicare pays 80% of the approved amount for most outpatient care and leaves you the other 20%, with no annual out-of-pocket cap. Part A adds a hospital deductible of $1,736 per benefit period in 2026, and that deductible can apply more than once in a year if you have separate hospital stays. Medigap caps that exposure.3

The Illinois birthday rule

Illinois gives Medigap policyholders an annual birthday rule, but its terms are specific. Under Illinois law, a Medigap policyholder who is at least 65 but no more than 75 years old is entitled to a 45-day open enrollment period each year, beginning on their birthday, during which they may switch without medical underwriting to a Medigap policy of equal or lesser benefits offered by the same insurer or an affiliate authorized to transact business in Illinois, according to the Illinois Department of Insurance (IDOI). During this window, rates may not discriminate in pricing because of your health status, claims experience, receipt of health care, or a medical condition.1

Compared with broader birthday rules in other states, Illinois adds two real limits. First, it is capped at ages 65 through 75, so a 78-year-old Illinois policyholder cannot use it. That age cap is unusual: California's birthday rule, for example, runs a 60-day window with no age cap and lets you move to any insurer. Second, the Illinois switch must stay with your current insurer or its affiliate; the rule does not let you move to an unrelated company without underwriting. Within those bounds, it is still a useful protection: if your insurer sells a less expensive equal-or-lesser plan, you can move into it once a year without proving you're healthy.2

The "equal or lesser benefits" limit is the key constraint. You can move sideways (Plan G to another Plan G the insurer offers) or down to a less generous letter (Plan G to Plan N), but the birthday rule does not let you move up to a more comprehensive plan. Moving up still requires medical underwriting outside a guaranteed-issue window.1

How to use the Illinois birthday rule

The window is short and the terms are narrow, so plan ahead.

Because the benefits inside a letter are standardized, a same-letter switch changes your premium, not your coverage. If you move to a lesser letter, your cost-sharing changes to match that letter.1

Plan G and Plan N: the common choices

For someone newly eligible for Medicare, the practical choice in Illinois narrows to two plans.

Plan G is the most complete plan still available to people who became eligible on or after January 1, 2020, and it is the most popular choice for newly eligible enrollees. It covers every gap in Original Medicare except the annual Part B deductible: the Part A hospital deductible, Part A and Part B coinsurance, skilled nursing facility coinsurance, and Part B excess charges. After you pay that one Part B deductible for the year, a Plan G holder generally has no further cost-sharing on Medicare-covered services.4

Plan N covers the same major gaps but shifts a little cost back to you. It pays the Part B coinsurance in full except for a copay of up to $20 for some office visits and up to $50 for emergency-room visits that don't lead to an inpatient admission, and it does not cover Part B excess charges. In exchange, Plan N premiums are usually lower than Plan G premiums.2

If a lower monthly premium matters more than paying costs up front, Illinois insurers also sell a high-deductible Plan G. It carries the same benefits as standard Plan G, but you pay Medicare-covered costs up to a deductible of $2,950 in 2026 before the policy begins to pay, in exchange for a lower premium.2

Plans C and F are closed to newer enrollees

Plans C and F once covered the annual Part B deductible on top of the other gaps, which made Plan F the most complete plan on the market. Under the Medicare Access and CHIP Reauthorization Act of 2015 (MACRA), any Medigap plan that pays the Part B deductible is closed to people who first became eligible for Medicare on or after January 1, 2020.4

The closure works by eligibility date, not purchase date. If you became eligible for Medicare before January 1, 2020, you can still buy or keep Plan C or Plan F in Illinois. If you became eligible on or after that date, those two plans are off the table, which is why Plan G has become the default top-tier choice for newer enrollees: it is identical to Plan F except that you pay the one Part B deductible yourself.4

When you can buy or switch in Illinois

Illinois gives you more than one protected window. These matter most.

• The federal Medigap Open Enrollment Period. This is a one-time, six-month window that begins the first month you are both age 65 or older and enrolled in Medicare Part B. During it, insurers must sell you any Medigap policy they offer at their best available rate regardless of your health, with no medical underwriting. This is the single best time to buy, because you can choose any plan, including Plan G.4
• The annual birthday rule. The 45-day window described above, repeating each year for policyholders ages 65 to 75, for switching to an equal-or-lesser plan from the same insurer or an affiliate with no underwriting.1
• Federal guaranteed-issue rights. Certain life events, such as losing other coverage or an insurer leaving the market, trigger a federal guaranteed-issue right to buy specific plans without underwriting.

Illinois also designates at least one insurer that must sell a Medicare Supplement policy to applicants age 65 and older year-round, regardless of health. Which company holds that designation is set each year, so confirm the current year's guaranteed-issue insurer with the Illinois Department on Aging before relying on it.5

Outside these windows, an Illinois insurer can require medical underwriting and charge more, or decline to sell you a policy, based on your health. That is why the choice between Plan G and Plan N is best made during your six-month open enrollment: the birthday rule won't cover a move up to a richer plan, and it ends at age 75, so underwriting could later make an upgrade expensive or impossible.

What Medigap costs and how it's priced in Illinois

Medigap premiums vary widely. The benefits inside a letter are fixed by the federal standard, so you are comparing price, service, and rate stability, not coverage. What you pay depends on the insurer, your age, and in many cases your gender and tobacco use.2

Insurers generally use one of three pricing methods, which shapes how your premium changes as you age. Ask which method an insurer uses, not just the first-year premium:

• Community-rated policies charge everyone the same premium regardless of age.
• Issue-age-rated policies base your premium on your age when you buy, and that starting point does not rise simply because you get older.
• Attained-age-rated policies start lower but increase as you age, so a low first-year quote can climb over time.

The Illinois birthday rule pairs only partially with cost control: it lets you move to a cheaper equal-or-lesser plan from the same insurer or an affiliate between ages 65 and 75, but it will not move you to an unrelated carrier or keep working after 75. Note that Medigap does not include prescription drug coverage, so you add a separate Medicare Part D plan for that.

Who regulates Medigap in Illinois

Illinois Medigap policies are regulated by the Illinois Department of Insurance, which oversees the insurers that sell these policies and handles consumer complaints. If you have a question or a complaint about a specific policy, that is the agency to contact.1

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The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.