Here is the Medicare decision that catches people off guard. A $0-premium Medicare Advantage plan is easy to get into. Getting back out of it, into a Medigap plan like Plan G, can be a lot harder than anyone tells you at 65.

I talk with people across Lexington, Columbia, Irmo, and Chapin who chose a Medicare Advantage plan a few years ago, mostly for the low premium, and now want to switch to a Medicare Supplement for the predictable costs and the freedom to see any doctor. Sometimes that switch is simple. Often it is not, because of one thing most folks never heard about when they signed up: medical underwriting. If you understand how this works, you can protect yourself. If you do not, you can get stuck.

The one window where switching is easy

There is exactly one time the door is guaranteed open. When you first turn 65 and enroll in Medicare Part B, you get a one-time, six-month Medigap Open Enrollment Period. During those six months, insurance companies have to sell you a Medigap plan at standard rates no matter what your health looks like. No health questions, no denials, no higher price for your conditions.

That window comes once in your lifetime, and when it closes, it does not come back. This is the single most important thing to understand about Medicare timing, and it is why the choice you make at 65 carries more weight than people realize.

After that window, most South Carolina switches go through underwriting

Here is where people get surprised. Outside that first six-month window, and outside a few specific situations covered below, a Medigap insurer in South Carolina is allowed to run your application through medical underwriting. That means they can ask about your health, and based on your answers they can charge you more, attach a waiting period for pre-existing conditions, or turn you down entirely.

South Carolina follows the federal rules here. A handful of states have passed their own laws, sometimes called birthday rules, that let people switch Medigap plans each year without health questions. South Carolina is not one of them. So for a retiree in the Midlands, once your initial window has passed, getting a Medigap plan usually depends on your health.

And the cruel part of the timing is this: the person who most wants to leave Medicare Advantage, the one who developed a heart condition, cancer, COPD, kidney disease, or diabetes with complications, is exactly the person underwriting is most likely to reject. The health event that makes you want predictable coverage is often the same one that blocks you from getting it. That is the trap.

Your one built-in do-over: the 12-month trial right

Federal law does give you one safety net, and it is worth knowing precisely how it works.

If you joined a Medicare Advantage plan when you first became eligible for Medicare at 65, you have a 12-month trial right. Within that first year, you can leave the Advantage plan and buy a Medigap policy with guaranteed issue, no health questions asked. There is also a version of this if you dropped a Medigap policy to try Medicare Advantage for the very first time. In that case you can switch back to that same Medigap policy within 12 months.

The catch is the calendar. This right lives inside the first year only. Miss it by a day and you are back in underwriting territory. If you are in your first year on an Advantage plan and having second thoughts, that is the time to act, not next year.

The other situations that open the door

Beyond the trial right, federal law creates a few more guaranteed-issue situations where an insurer cannot underwrite you. The most common ones for people leaving Medicare Advantage:

• Your Advantage plan leaves Medicare or stops serving your area
• You move outside your plan's service area
• Your plan seriously breaks its contract or misled you about coverage

In these cases you generally get a 63-day window to buy a Medigap policy on a guaranteed-issue basis, starting when your Advantage coverage ends. If one of these happens to you, keep every letter and notice the plan sends. You may need that paperwork to prove you have the right. And do not let the 63 days slip by, because missing the window can cost you the protection even when the change was completely out of your hands.

What "underwriting" actually means

If none of the guaranteed-issue situations apply, you can still try to switch. You just have to qualify. The insurer reviews your health history and decides. Conditions that commonly lead to a decline or a higher rate include heart disease, diabetes with complications, COPD, a recent cancer diagnosis, kidney disease, and a history of stroke.

Here is the encouraging part, though. A no from one company is not a no from all of them. Every Medigap carrier sets its own underwriting standards, and one may be comfortable with a condition that another rejects. This is exactly where working with an independent agent helps, because we know which carriers tend to be more forgiving on which conditions, and we can point your application where it has the best chance instead of guessing.

If you do switch, do it in the right order

When a switch is possible, the sequence matters, and getting it wrong can leave you with a coverage gap.

Apply for the Medigap policy and get approved first, before you drop your Medicare Advantage plan. Do not cancel anything until the new coverage is locked in. Once your Medigap policy is approved, you can disenroll from the Advantage plan during a valid window, and time the Medigap start date so there is no gap.

One more piece people forget: Medicare Advantage usually includes your drug coverage, so when you move to Original Medicare plus Medigap, you also need to pick up a standalone Part D prescription plan. Do not skip it. Going without creditable drug coverage for 63 days or more can trigger a Part D late penalty that follows you permanently.

This is why the first choice matters so much

None of this is a reason to avoid Medicare Advantage. For plenty of healthy retirees focused on a low premium, it is a reasonable choice. The point is that the decision is not as easy to reverse as it looks, so it deserves real thought up front rather than a quick pick based on premium alone.

If you are weighing the two right now, it helps to see the full comparison before you decide. Our guide on [Medicare Advantage vs. Medigap in South Carolina] walks through the cost and coverage differences, and if you are deciding between the top supplement options, [Plan G vs. Plan N] breaks those down. If you are just approaching 65, [Turning 65 in Lexington, SC: the Medicare deadlines that matter] covers the timing that protects windows like the one above.

Not sure where you stand? Let us look at it with you

As an independent agency based in Lexington, we help Medicare clients across the Midlands figure out their real options, including whether you can still qualify for a Medigap plan and which carriers give you the best shot. If you are thinking about leaving a Medicare Advantage plan, or you just want to understand your window before you make a move, call or text us for a free, no-pressure review.

The best time to protect your options is before you need them. If you are not sure whether your window is still open, that is worth a conversation now rather than later.

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We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Program (SHIP) to get information on all of your options.

This article is general information, not legal advice. Medicare rules and enrollment windows can change, so confirm current details before making a decision.