Missouri Medicare Supplement Rules: The Anniversary-Rule advantage.

Most states make it hard to change Medicare Supplement plans after your first six months on Medicare. Once you're past your initial open enrollment period, you usually have to pass medical underwriting to switch — and if your health has changed, you may not qualify, or your premium may jump.

Missouri is different. Missouri has one of the friendliest Medigap rules in the country, and most of the folks we work with here have no idea it exists.

It's called the Missouri Anniversary Rule, and if you own a Medicare Supplement policy in Missouri, you should know how to use it.

What the Anniversary Rule actually says

The Missouri Anniversary Rule (sometimes called the "birthday rule," though it's tied to the policy date, not your birthday) is part of Missouri insurance regulation. It says:

• For 30 days before and 30 days after the anniversary date of your existing Medicare Supplement policy,
• you can switch to a different carrier's Medicare Supplement policy of the same letter (Plan G to Plan G, Plan N to Plan N, etc.),
• without medical underwriting,
• and the new carrier has to accept you at their standard rates for your age and rating class.

The anniversary date is the calendar day your current Supplement policy went into effect — not your birthday and not the policy renewal date. If your policy started July 15, your annual anniversary window is roughly June 15 through August 14 each year.

Why this is unusual

In most states, once you're past your six-month initial Medigap open enrollment period (the window that starts the day Part B becomes effective for you), changing Supplement plans requires underwriting. The new carrier reviews your medical history, your current prescriptions, and your recent procedures. If you've had a heart event, a cancer diagnosis, or even a couple of common chronic conditions on the wrong list, you may be declined or rate-classed up.

Missouri's rule means Supplement holders here have a yearly chance to shop the market and switch to a better-priced carrier on the same letter plan, no matter what's happened to their health since they enrolled.

A few other states have similar windows — Oregon, California, Idaho, and Washington use birthday-month rules with different mechanics. Most states have no such rule at all. Missouri's is one of the better ones.

How to use the rule

The mechanics are straightforward.

We help clients run this annually. It's a 30-minute conversation. Sometimes the switch saves real money. Sometimes the current carrier is already competitive and there's nothing to switch to. Either way, the review is worth doing.

The other no-underwriting doors

The Missouri Anniversary Rule isn't the only way to get a Medicare Supplement without underwriting. Federal Medigap rules give you guaranteed issue rights in several scenarios:

• You're in the 6-month initial Medigap open enrollment period that starts when your Part B becomes effective. (The biggest one — most people get their first Supplement during this window.)
• You lose employer coverage (yours or a spouse's) and need supplemental coverage.
• Your Medicare Advantage plan terminates, leaves the area, or you move out of its service area.
• You enrolled in Medicare Advantage when you first became eligible and want to switch back to Original Medicare within 12 months (the "trial right").
• You move to a new area where your current Supplement isn't sold.
• Your current Supplement carrier becomes bankrupt or your policy ends through no fault of your own.

In each of those cases, federal law guarantees you a Supplement at standard rates with no underwriting, regardless of your state. The Missouri Anniversary Rule is in addition to these — it's the once-a-year "shop the market" right.

When not to switch

The anniversary review isn't always a switch. A few reasons we sometimes tell a client to stay put:

• The premium difference is small. A $5–10/month difference may not be worth the carrier-change paperwork.
• The new carrier's recent rate-increase history is worse than the current carrier's. A lower 2026 premium that climbs faster in 2027 and 2028 isn't actually cheaper.
• The current carrier has good customer service and you've had no issues — that's worth something.
• You're in the middle of a complex claim or care transition where stability matters more than savings.

The point of the review is to decide. Sometimes the decision is to stay.

Medigap plan letters in 2026

A quick recap on the Supplement plan letters that matter most in 2026:

The anniversary rule applies to whatever letter plan you currently have — you can only switch to the same letter, not a different letter. (To switch letters, you'd need underwriting, except in a guaranteed-issue scenario above.)

Use it once a year — that's the whole pitch

The Missouri Anniversary Rule is one of the most underused tools we see in our market. People with Supplements paid into them for years without realizing they could shop the market annually without underwriting.

If you're a Missouri Medigap holder, mark your anniversary date on your calendar. Sixty days a year, the door is open. Sometimes you walk through it, sometimes you don't, but knowing the door is there matters.

I've been helping people in St. Louis with Medicare since 2013. The anniversary review is part of every annual conversation we have with Supplement clients — and we'll do it for free for anyone in Missouri, whether or not we wrote the original policy.

No fee, no pressure, no sales pitch — that's the rule of the house. We answer every call.