A client came to me a few years back — I'll call her Diane — seventy-one, recently widowed, and frightened by a hospital bill. She'd had a cardiac procedure, Medicare had paid its share, and she was staring at her 20% coinsurance with no idea it had no ceiling. "I thought Medicare covered everything," she said. It doesn't. And the insurance designed to cover that gap, Medigap, was now going to cost her far more than it should have — because she'd passed up the one window when she could have bought it without a single health question.
Let me be direct about this. Medigap is one of the most valuable financial products available to a retiree, and also one of the most misunderstood. The plan letters confuse people. The enrollment rules are unforgiving. And the single most important fact about it has nothing to do with which plan you pick. It has to do with when you buy. I've watched too many people learn that the hard way, so let's get it right.
What Medigap Actually Is
Medigap — the formal name is Medicare Supplement Insurance — is private insurance you buy to fill the gaps in Original Medicare (Parts A and B). When you have a covered service, Medicare pays first, then your Medigap policy pays its share of what's left. That's the whole job. It does one thing, and for most people it does it well.
Here's why it matters so much. Original Medicare has no annual out-of-pocket maximum. None. Part B generally pays 80% of approved costs and leaves you the other 20% — and that 20% keeps running with no cap, year after year. On a routine year that's an annoyance. On the year you have heart surgery or a cancer diagnosis, it's the difference between a manageable expense and a five-figure one. Medigap is what turns that open-ended risk into a predictable number.
What it does not cover is just as important. Medigap pays nothing toward prescription drugs — you need a separate Medicare Part D plan for that, and skipping it can trigger a lifelong late-enrollment penalty. It also doesn't cover dental, vision, hearing aids, or long-term custodial care. Medigap is a supplement, not a Swiss Army knife. Know what it's for.
The Plans: Start With G and N
The part that intimidates everyone is the alphabet — Plans A, B, C, D, F, G, K, L, M, and N. Here's the good news, and it's a relief once you understand it: these plans are standardized by federal law. A Plan G from a tiny insurer covers exactly the same benefits as a Plan G from a giant national carrier. The only things that differ are the price and the company's service. That means your job is not to decipher ten products. It's to pick a letter, then shop that letter on price.
For anyone shopping today, the conversation almost always comes down to two letters. Plan G is the most comprehensive plan available to new enrollees — it covers everything except the annual Part B deductible ($283 in 2026, an amount you'll pay once a year and then forget about). Plan N covers nearly as much but asks you to pay small copays — up to $20 for an office visit, up to $50 for an emergency room visit that doesn't lead to admission — and doesn't cover the rare "Part B excess charge" some doctors add. In exchange, Plan N's premium typically runs $20 to $50 a month less. For a healthy person who doesn't see specialists constantly, Plan N is often the better value; in the handful of states that ban excess charges outright, it's close to a no-brainer.
A word on Plan F, because people still ask for it by name. Plan F was the Cadillac plan that covered every gap, including the Part B deductible. Under a 2015 federal law (MACRA), it closed to anyone who became eligible for Medicare on or after January 1, 2020. If you were eligible before that date, you may still be able to buy it; if you already have it, you can keep it. But for most people reading this, Plan F is simply off the menu, and Plan G is its natural successor. There's also a high-deductible version of Plan G — a much lower premium in exchange for a $2,950 deductible in 2026 — which can make sense for healthy retirees comfortable carrying that risk.
The Six-Month Window That Decides Everything
If you remember nothing else from this article, remember this section. This is where the real money is won or lost, and it's the part Diane got wrong.
You get one Medigap Open Enrollment Period in your life. It's six months long, and it starts automatically the month you are both 65 or older and enrolled in Medicare Part B. During those six months, federal law gives you what's called guaranteed issue: any insurer must sell you any Medigap plan they offer, cannot ask you a single health question, and cannot charge you more because of your medical history. A cancer survivor and a marathon runner pay the same rate. It is the one moment the deck is stacked in your favor.
Here's the trap. That window does not come back. Outside of it — and outside a few specific protected situations — insurers in most states are free to put you through medical underwriting. They can review your health, charge you more, make you wait, or deny you outright. I've seen retirees in good health at 65 assume they could pick up Medigap "later if I need it," then develop a heart condition at 68 and discover that later is exactly when no carrier will issue them a policy at a fair price. The time to buy is when you're healthy and the door is open, not when you're sick and it's closing.
There are a handful of escape hatches, called guaranteed-issue rights, that reopen the door for 63 days: if an employer plan you were relying on ends, if your Medicare Advantage plan leaves the program or your area, or if you're using a one-time, 12-month "trial right" to leave Medicare Advantage after first joining it. A growing number of states have also added their own protections — New York and Connecticut allow continuous year-round switching without underwriting, while others such as Massachusetts and Maine offer narrower annual windows, and states including California and Oregon now have "birthday rule" periods to change plans. These rules vary and change often, so check your own state's current law before you count on one. But the safest plan by far is simple: buy during your six-month window and don't gamble on the exceptions.
What It Costs — and the Pricing Trap
Let's talk real numbers, with the honest caveat that Medigap premiums vary enormously by state, age, insurer, and even tobacco use. As a national ballpark for a 65-year-old, Plan G commonly runs somewhere in the range of $150 to $250 a month, and Plan N a bit less — but high-cost states can push Plan G well past $300. Two people the same age, same plan, one ZIP code apart, can pay very different premiums. Always get several quotes for the same plan letter; because the benefits are identical, the cheapest reputable carrier is genuinely the best buy.
What trips people up isn't the starting price — it's how the price changes. There are three ways insurers set Medigap premiums, and the difference matters for decades:
- Community-rated. Everyone in the area pays the same premium regardless of age. Your rate won't climb just because you're getting older.
- Issue-age-rated. Your premium is based on your age when you bought in, and locks there. Buy younger, pay less for life.
- Attained-age-rated. Your premium is based on your current age and rises every year as you get older — on top of normal inflation increases.
Attained-age plans are the most common, and they're the quiet trap. The premium that looks like a bargain at 65 can become genuinely unaffordable by 78 or 80 — precisely the age when underwriting makes it hardest to switch to something cheaper. (Yes, even I have watched clients get cornered by this, and it still frustrates me.) Before you sign, ask the agent one direct question: "Which pricing method is this, and what have your rate increases looked like over the last five years?" The answer tells you more than the first-year premium ever will.
Medigap or Medicare Advantage?
This is the fork in the road, and there's no universally right answer — only the right answer for you. Medicare Advantage replaces Original Medicare with a private plan, usually with a low or $0 premium and bundled drug and dental coverage. Medigap sits on top of Original Medicare, costs more in premium, and requires a separate drug plan. So why pay more?
Three reasons, in my experience. First, freedom: with Original Medicare plus Medigap, you can see any doctor or hospital in the country that accepts Medicare — no networks, no referrals, no prior-authorization fights. Second, predictability: once you've paid your premium and the small Part B deductible, a Plan G leaves you with almost nothing to pay. Medicare Advantage, by contrast, charges you per service up to an annual maximum that reaches $9,250 in-network in 2026 — fine in a healthy year, painful in a bad one. Third, and this is the part people don't see coming: leaving Advantage for Medigap later usually means facing underwriting. The low-premium plan you chose at 65 can become a cage if your health changes and no Medigap carrier will take you.
Let me be direct. Medicare Advantage can be an excellent choice for someone who values low premiums, stays in-network, and is comfortable with the system's rules. But if your top priorities are choice of doctors and a cost you can plan around — and especially if you'd struggle to pass a health screening down the road — the case for buying Medigap during your open enrollment window is strong. If you do plan to switch out of Advantage, get your Medigap approval in hand before you drop the Advantage plan, not after.
The Mistakes I See Most — and Your Next Step
After many years of these conversations, the same handful of errors come up again and again:
- Missing the six-month window because Part B was delayed or the timing was misunderstood. It starts when you're 65 and enrolled in Part B — mark it on a calendar.
- Assuming you can switch anytime. Outside protected windows, most states allow underwriting. You can't count on changing your mind later.
- Forgetting Part D. Medigap covers no drugs. Pair it with a Part D plan or face penalties.
- Buying on first-year price alone without asking whether it's an attained-age plan that will climb.
- Choosing Advantage at 65 with no plan for how you'd ever get back to Medigap if your health declines.
None of this is beyond you. If you're approaching 65, find out the exact start date of your Medigap Open Enrollment Period, decide between Plan G and Plan N, and get three quotes for that letter before the window opens. If you're already past it, you still have options — check whether your state offers year-round or birthday-rule switching, and compare what underwriting would cost you. And if you want a neutral second opinion, your State Health Insurance Assistance Program (SHIP) offers free, unbiased Medicare counseling; you can reach it at 1-800-MEDICARE.
Diane, for what it's worth, got there. We found her a solid Plan N, sorted out a Part D plan, and she hasn't been blindsided by a hospital bill since. It cost her more than it should have because of the timing — but she stopped lying awake over the next procedure. That peace of mind is the whole point. You've navigated harder decisions than this one, and you don't have to make it alone.
