If you have a Medicare Supplement — also called Medigap — policy, you already know how valuable it is for covering the gaps that Original Medicare leaves behind. What many beneficiaries don't realize is that in most of the country, once you're enrolled in a Medigap plan, switching to a different one means going through medical underwriting. That means an insurer can review your health history, charge you significantly higher premiums because of pre-existing conditions, or outright deny your application. But in 13 states, a policy called the birthday rule changes that equation entirely — and if you live in one of those states, it may be one of the most powerful consumer protections you've never heard of.
The birthday rule gives Medigap policyholders a 30-day window each year, starting on their birthday, to switch to a Medicare Supplement plan with equal or lesser benefits — without any medical underwriting. That means an insurer cannot ask about your health history, cannot charge you a higher premium because you have diabetes or heart disease, and cannot deny your application. The window is typically 30 days, though some states extend it slightly. The states that currently have this protection in place are California, Idaho, Illinois, Kentucky, Louisiana, Maine, Maryland, Missouri, Nevada, New Jersey, New York, Oklahoma, and Oregon. New York operates under continuous guaranteed issue rules that go even further, allowing residents to switch Medigap plans at any time without underwriting, making the birthday rule somewhat redundant there — but the protection exists nonetheless.
To understand why this matters so much, consider what happens in states without the birthday rule. When you first turn 65 and enroll in Medicare Part B, you have a six-month open enrollment window during which insurers must sell you any Medigap plan they offer at standard rates, regardless of your health. Once that window closes, you're largely on your own. If you want to switch from Plan N to Plan G, or from one insurer to another offering a lower premium for the same plan, the new insurer can put you through full medical underwriting. For someone managing chronic conditions — which describes the majority of Medicare beneficiaries — that can mean premium surcharges of 20% to 50% or outright denial. The birthday rule eliminates that barrier, at least for lateral or downward moves.
Here's how the birthday rule works in practice. Say you live in California and your birthday is June 15. Starting June 15, you have 30 days — until July 15 — to apply for a new Medigap plan with equal or lesser benefits from any insurer licensed in your state. You're currently on Plan G? You can switch to another insurer's Plan G, or move to Plan N, which has lower premiums but requires cost-sharing like a $20 copay for office visits and up to $50 for emergency room visits that don't result in inpatient admission. You cannot use the birthday rule to move from Plan N up to Plan G, because that would be upgrading your benefits. The rule is specifically designed to let you shop for better pricing or service on comparable coverage, not to expand your benefits without health screening.
The financial opportunity here is real. Medigap premiums vary significantly between insurers even for identical plans. In 2025, Plan G premiums for a 70-year-old woman in Los Angeles ranged from roughly $130 per month to over $220 per month depending on the insurer — for the exact same coverage. That's a difference of more than $1,000 per year. The birthday rule lets California residents shop that spread every single year without worrying about their health status disqualifying them. Over a five-year period, switching to a lower-cost insurer offering identical Plan G coverage could mean $5,000 or more in premium savings, depending on how aggressively rates diverge.
If you live in one of the 13 birthday rule states, the practical steps are straightforward. About 60 to 90 days before your birthday, start comparing Medigap plans on your state's insurance department website or through Medicare.gov's Medigap plan finder tool. Look specifically at plans with equal or lesser benefits to your current plan. Contact insurers directly or work with a licensed independent Medicare insurance broker — someone who represents multiple carriers, not just one. Get quotes in writing. Once your birthday arrives, you have 30 days to submit your application. Do not cancel your existing policy until your new coverage is confirmed in writing, because you want to avoid any gap in coverage.
For beneficiaries in states without the birthday rule, the options are narrower but not nonexistent. Federal law guarantees you the right to switch Medigap plans without underwriting in specific situations called Special Enrollment Periods or guaranteed issue rights. These include losing coverage through an employer or union plan, moving out of a Medicare Advantage plan's service area, or having your current Medigap insurer go bankrupt or leave the market. If your Medicare Advantage plan is discontinued at the end of the year — which happens regularly during the Annual Enrollment Period from October 15 through December 7 — you may qualify for guaranteed issue rights to purchase certain Medigap plans. These rights are time-sensitive, typically lasting 63 days from the triggering event, so acting quickly is essential.
Some states are actively considering adopting birthday rule protections. Advocacy organizations have pushed for broader adoption, arguing that the current patchwork system creates an unfair two-tier market where beneficiaries with health conditions in non-birthday-rule states are effectively locked into their current plan and insurer regardless of price increases. If your state is not on the current list, contacting your state insurance commissioner's office to ask about pending legislation is a reasonable step. Your state insurance department can also tell you about any state-specific Medigap protections that may exist outside the birthday rule framework.
One important nuance: the birthday rule applies to Medigap plans, not Medicare Advantage plans. If you're enrolled in a Medicare Advantage plan — the private insurance alternative to Original Medicare — different rules apply. Medicare Advantage has its own enrollment periods, including the Annual Enrollment Period each fall and the Medicare Advantage Open Enrollment Period from January 1 through March 31 each year, during which you can switch plans or return to Original Medicare. The birthday rule is exclusively a Medigap protection.
Finally, be aware that even within birthday rule states, not every insurer is required to offer every plan type. Some insurers may not sell Plan G or Plan N in your county. The Medicare.gov plan finder tool, updated annually, is the most reliable way to see which plans are available in your specific ZIP code. Your State Health Insurance Assistance Program — known as SHIP — offers free, unbiased counseling from trained volunteers who can walk you through your options without trying to sell you anything. To find your local SHIP office, visit shiphelp.org or call 1-800-MEDICARE.