Illinois Medicare Supplement underwriting rules: birthday rule, Blue Cross guaranteed issue, and everything in between

Illinois gives Medigap enrollees more flexibility than most states — but less than you might think. The Illinois Medicare Supplement underwriting rules include a birthday rule, a unique guaranteed issue carrier, and stronger protections for disabled beneficiaries under 65. But the birthday rule has limits that catch people off guard, and understanding those limits is the difference between a smooth plan change and a frustrating dead end.

Unlike states such as Texas, Georgia, and North Carolina — which follow federal rules only — Illinois has layered additional protections on top of the federal baseline. And unlike New York and Connecticut, where you can switch plans any day of the year with no questions asked, Illinois falls somewhere in the middle. Here’s exactly how the Illinois Medicare Supplement underwriting rules work.

The Illinois birthday rule: what it does and doesn’t do

Illinois enacted its Medigap Birthday Law through Senate Bill 56, signed in May 2024 and effective May 2025. It gives certain Medigap policyholders a 45-day window starting on their birthday each year to switch plans without medical underwriting. But the details matter — and this is where most people get the wrong impression.

Here’s how the Illinois birthday rule actually works:

• Window length: 45 days, starting on your birthday
• Age eligibility: 65 through 75 only — if you’re 76 or older, the birthday rule does not apply to you
• Plan switching: equal or lesser benefits only (you can move from Plan G to Plan N, but not from Plan N to Plan G)
• Carrier restriction: same insurance carrier or its affiliates/subsidiaries only — you cannot switch to a different company
• Must already have Medigap: you need an active Medigap policy to use this rule

Illinois birthday rule vs. Indiana birthday rule

Because both states border each other and many people split time between them, the comparison is worth spelling out clearly:

The key takeaway: Indiana’s rule lets you shop between carriers but keeps you on the same plan letter. Illinois lets you change plan letters but keeps you with the same carrier. Neither state matches the freedom of New York or Connecticut, where you can change both the carrier and the plan letter at any time.

Blue Cross Blue Shield of Illinois: year-round guaranteed issue

Illinois has something no other state on my licensed list has — a carrier that offers guaranteed issue Medigap enrollment year-round, regardless of your health. Blue Cross Blue Shield of Illinois is designated as a guaranteed issue company in 2026, meaning they must accept your Medigap application at any time of year without medical underwriting, at the same rate as anyone else in the same policy class.

This is a significant safety net. If you miss your initial open enrollment window, if you’re over 75 and the birthday rule no longer applies, or if you need to switch from Medicare Advantage to Medigap and don’t have a guaranteed issue right — BCBS of Illinois is an option that won’t turn you away.

Two important caveats: BCBS of Illinois also offers plans that do require underwriting alongside their guaranteed issue plans, so make sure you’re applying for the right one. And their premiums may be higher than competitors precisely because they accept all applicants — similar to the pricing dynamic in New York and Connecticut where year-round acceptance pushes premiums up.

The initial 6-month open enrollment period

Like every state, Illinois residents get a one-time, six-month Medigap Open Enrollment Period starting the first day of the month they turn 65 and are enrolled in Medicare Part B. During this window, the Illinois Medicare Supplement underwriting rules are entirely in your favor — every carrier must accept you, no health questions, no denials, no rate-ups based on pre-existing conditions.

This window is critical in Illinois because once it closes, your options narrow. Yes, the birthday rule gives you some flexibility between 65 and 75 — but only within your current carrier. And after 75, that protection disappears entirely (with the exception of BCBS of Illinois guaranteed issue and federal guaranteed issue rights). Getting the right plan and carrier during your initial window is more important in Illinois than in states like Connecticut where you can switch freely at any time.

What happens after the window closes (and after 75)

Outside of your initial open enrollment, your birthday rule window (ages 65-75), and any federal guaranteed issue right, the Illinois Medicare Supplement underwriting rules revert to standard medical underwriting. Carriers can:

• Ask health questions and review medical records
• Deny your application based on health conditions
• Charge higher premiums based on your health status
• Impose pre-existing condition waiting periods

This is particularly important for Illinois residents over 75. Once you age out of the birthday rule, your only paths to a new Medigap plan without underwriting are BCBS of Illinois guaranteed issue or a federal guaranteed issue event. If you’ve been putting off a plan change, your 75th birthday is a real deadline to be aware of.

Federal guaranteed issue rights in Illinois

The same federal guaranteed issue rights that apply in Georgia, Texas, and every other state also apply in Illinois. These include:

• Loss of employer or retiree coverage — apply within 63 days
• Medicare Advantage plan leaves your area or stops operating
• 12-month MA trial right — first-time MA enrollees at 65 can switch back to Original Medicare plus Medigap within 12 months
• Medigap carrier misled you or went bankrupt
• Loss of Medigap coverage through no fault of your own

Illinois also offers a 6-month guaranteed issue window for people leaving Medicare Advantage plans, which goes beyond the federal minimum. If you’re dropping a Medicare Advantage plan and returning to Original Medicare in Illinois, you have six months of guaranteed access to Medigap — a stronger protection than most states provide.

Under-65 Medicare beneficiaries in Illinois

Illinois stands out here. The state requires Medigap carriers to offer plans to Medicare beneficiaries under 65 who qualify due to disability, with the same enrollment rights as those 65 and older. Premiums for under-65 enrollees are capped at the highest rate charged to those over 65 — meaning carriers cannot impose the dramatically inflated premiums that are common in states like Georgia.

Additionally, under-65 beneficiaries who did not purchase a Medigap plan during their initial open enrollment get a second chance: they can enroll in a BCBS of Illinois Medigap plan during the October 15 to December 7 window each year. And when they turn 65, they get an additional six-month Medigap Open Enrollment Period — a fresh guaranteed issue window on top of the one they had when they first became eligible.

How Medigap pricing works in Illinois

Illinois allows carriers to use any of the three standard pricing methods:

• Attained-age rating — most common in Illinois. Premiums rise as you age, in addition to carrier-wide rate increases.
• Issue-age rating — premium set at the age you first buy the policy. Doesn’t increase with age, though inflation adjustments still apply.
• Community rating — everyone pays the same premium regardless of age. Less common in Illinois but required in states like New York and Connecticut.

Because the birthday rule restricts you to your current carrier, your initial carrier choice in Illinois matters even more than in states with cross-carrier switching. A carrier with a lower starting premium but aggressive rate increases could cost you more over time — and the birthday rule won’t let you escape to a competitor.

Illinois Medicare Supplement underwriting rules at a glance

Major Medigap carriers active in Illinois

Illinois has one of the largest Medigap markets in the country with 49 carriers serving nearly 788,000 enrollees. Because plan benefits are federally standardized, the differences between carriers come down to premium, rate stability, customer service, and financial strength. Active carriers include:

• Blue Cross Blue Shield of Illinois (guaranteed issue option)
• AARP / UnitedHealthcare
• Mutual of Omaha
• Cigna
• Aetna
• Transamerica
• Philadelphia American

With the birthday rule limiting you to your current carrier, your initial carrier choice is one of the most consequential decisions you’ll make. An independent advisor who is appointed with multiple carriers can compare rate increase histories and help you choose a carrier you’ll want to stay with for the long haul.

How to protect yourself under Illinois’ rules

1. Choose your initial carrier wisely

Because the birthday rule only lets you switch within the same carrier family, your first carrier choice effectively determines your options for the next decade or more. Look at five-year rate increase history, not just today’s premium. A carrier that starts $20 cheaper but raises rates 12% annually will cost you far more than a stable carrier that starts slightly higher.

2. Use the birthday rule strategically between 65 and 75

If your premiums are climbing and you’re between 65 and 75, your birthday window is the time to consider downgrading from Plan G to Plan N within the same carrier. Plan N has lower premiums in exchange for small copays on office visits and ER trips. For someone who rarely uses medical services, this can save real money without giving up catastrophic protection.

3. Know your BCBS of Illinois safety net

If you’re over 75, if you have health conditions that make underwriting risky, or if you need Medigap coverage outside of any protected window — BCBS of Illinois guaranteed issue plans are your backup option. The premium may be higher than other carriers, but guaranteed acceptance when you need it is valuable insurance in itself.

4. Don’t wait until 76 to act

Your last birthday rule window is at age 75. If you’ve been thinking about a plan change, do it before you turn 76. After that, your only options without underwriting are BCBS of Illinois and federal guaranteed issue events.

How Illinois compares to other states

Illinois sits in a middle tier — better than states with no additional protections at all, but not as strong as the states that offer year-round open enrollment. Florida, Texas, Georgia, Ohio, Pennsylvania, and South Carolina have no birthday rule at all — once the initial window closes, it’s underwriting or nothing.

Indiana’s birthday rule is more generous in some ways — 60 days instead of 45, no age cap, and open to any carrier — but it restricts you to the same plan letter, while Illinois lets you change plan letters within the same carrier. New York and Connecticut remain in a class of their own with year-round switching to any plan from any carrier.

Illinois’ unique BCBS guaranteed issue option adds a safety net that most states lack entirely. Combined with stronger under-65 protections and the expanded MA-to-Medigap window, the Illinois Medicare Supplement underwriting rules offer a more layered set of protections than they first appear — but only if you understand how to use each one strategically.

For a full comparison of how every state where I’m licensed handles Medigap underwriting, see our Medicare Supplement Underwriting Rules by State guide.