They Cover Completely Different Things — And You Probably Need Both
Medicare Supplement (also called Medigap) and Part D are two separate products that cover two separate parts of your healthcare costs, and buying one does not get you the other. That’s the short answer. But I’ve watched people spend years paying way more than they should because nobody explained this clearly from the start, so let me give you the full picture.
Original Medicare — Parts A and B — covers hospital stays and doctor visits, but it leaves you with significant cost-sharing: deductibles, coinsurance, and no out-of-pocket maximum. A Medicare Supplement plan covers those gaps. Part D is an entirely different animal. It covers prescription drugs, which Original Medicare mostly doesn’t cover at all. These aren’t competing products. They’re filling different holes.
Here’s a quick side-by-side before we go deeper:
| Feature | Medicare Supplement (Medigap) | Part D |
|---|---|---|
| What it covers | Medicare cost-sharing (deductibles, coinsurance, copays) | Prescription drugs |
| Sold by | Private insurance companies | Private insurance companies |
| Standardized? | Yes — Plan G is Plan G everywhere | No — formularies vary widely by plan |
| Works with | Original Medicare (Parts A and B) | Original Medicare or Medicare Advantage |
| Monthly premium | Typically $100-$200/month at age 65 (varies by state) | Typically $10-$60/month for basic coverage |
| Can you skip it? | Yes, but you’re exposed to unlimited cost-sharing | Skip it and face a late enrollment penalty later |
What Medicare Supplement Actually Pays For
When you use Medicare-covered services, Original Medicare pays its share and then leaves you with the rest. That “rest” is what Medigap covers. Think of it as filling the gaps in Original Medicare’s coverage, which is literally where the name comes from.
For 2026, the Part A deductible is $1,676 per benefit period. That means if you’re hospitalized twice in a year and they’re counted as separate benefit periods, you could owe that amount twice. The 2026 Part B deductible is $257, and after that you owe 20% of every Medicare-approved doctor and outpatient service. There’s no cap on that 20%. None. A 67-year-old in Ohio with a serious diagnosis could owe tens of thousands of dollars in Part B coinsurance alone.
The most popular Medigap plan right now is Plan G. It covers the Part A deductible, all Part B coinsurance, skilled nursing facility coinsurance, and more. The only thing it doesn’t cover is the Part B deductible ($257 in 2026). After that, your out-of-pocket costs for Medicare-covered medical care are essentially zero. That’s the appeal. You pay your monthly premium, you show your Medicare card anywhere in the country that takes Medicare, and the bill gets handled.
What Plan G does not cover: dental, vision, hearing, or prescription drugs. Those require separate coverage entirely.
What Part D Actually Pays For
Original Medicare Part A and Part B cover almost no outpatient prescription drugs. There are narrow exceptions, like certain drugs administered in a clinical setting, but the medications you pick up at a pharmacy are not covered by Original Medicare at all. That’s why Congress created Part D in 2006 and why you need it as a separate product.
Part D plans are sold by private insurers and each one has its own formulary, which is a list of covered drugs. Two plans from the same insurer can cover the same drug at wildly different cost-sharing levels. This is where Part D gets complicated, and it’s worth actually comparing plans each year during open enrollment rather than auto-renewing. A plan that worked great for you when you were on two generics might become expensive if you add a specialty medication.
One thing that changed significantly with the Inflation Reduction Act: starting in 2025, out-of-pocket drug costs under Part D are capped at $2,000 per year. That’s genuinely good news, especially for anyone on expensive specialty drugs who previously faced catastrophic-phase costs.
Part D does not cover anything on the medical side. It won’t help with your Part B coinsurance, your hospital deductible, or any other Medicare cost-sharing. That’s Medigap’s job.
The Mistake I See Over and Over Again
Here’s the one that really gets me. People sign up for a Medicare Supplement plan, feel covered, and then skip Part D because they think, “I don’t take many medications, so I’ll just pay out of pocket when I need something.”
That thinking is understandable, but it has a trap built in. If you don’t enroll in Part D when you’re first eligible and you don’t have other qualifying drug coverage, Medicare will charge you a late enrollment penalty for every month you were without coverage. That penalty is permanent. It gets added to your Part D premium for as long as you have Medicare. For someone who waits five years, we’re talking about a 60% surcharge on your drug premium, every month, for the rest of your life.
I’ve talked to people in their mid-70s who are paying noticeably higher premiums because they skipped Part D for three or four years in their 60s when they were healthy and didn’t need many drugs. They figured they’d add it when they needed it. By then the damage was done.
The math almost never works in your favor when you skip Part D early. Even a bare-bones plan for $15 to $20 a month protects you from the penalty and keeps your options open. If your prescriptions are cheap generics, you might not even use it much. But having it on the books matters.
The same principle applies in reverse: don’t assume a Medigap plan covers your medications. I’ve had people tell me their Plan G “should” cover a $400 prescription because they paid their premiums and the plan is supposed to cover everything. It doesn’t. Plan G covers Medicare cost-sharing. Drugs are Part D’s territory.
How They Work Together (And When Medicare Advantage Changes the Equation)
If you have Original Medicare, the typical setup that makes sense for most people is this: Medicare Parts A and B, plus a Medigap plan like Plan G, plus a standalone Part D plan. These three layers work together cleanly. Medicare pays first, Medigap picks up the cost-sharing, and Part D handles your prescriptions through your pharmacy.
Medicare Advantage changes this. If you choose Medicare Advantage (Part C) instead of Original Medicare plus Medigap, you cannot use a Medigap plan. These two are not compatible. Medicare Advantage plans often include drug coverage built in, which is why you’ll hear them called MAPD plans. In that case, you don’t add a separate Part D plan because it’s already included.
This distinction trips people up. Someone switches from a Medigap setup to Medicare Advantage, then tries to keep their old Part D plan separately. It doesn’t work that way. When you’re in Medicare Advantage, the plan manages everything, drug coverage included (assuming it’s an MAPD plan).
My honest take on Medicare Advantage versus Medigap is a longer conversation, but the short version is this: for people who travel, have ongoing health conditions, or want predictable costs and wide doctor access, Medigap plus Part D is usually the more dependable setup. Medicare Advantage can be a reasonable choice for healthier people who stay in-network and want lower upfront premiums. But that’s a separate article.
Bottom Line
Medicare Supplement and Part D are not optional add-ons you pick between. For most people on Original Medicare, you need both: Medigap to protect you from medical cost-sharing, and Part D to cover your prescriptions. Skipping either one because you’re healthy right now is a gamble that tends to look worse in hindsight. If you’re turning 65, get Plan G and a standalone Part D plan in place during your initial enrollment window, and revisit the Part D plan every fall during open enrollment to make sure it still covers your medications well.
Frequently Asked Questions
Can I use my Medicare Supplement plan to pay for prescriptions at the pharmacy?
No. A Medigap plan like Plan G covers Medicare cost-sharing for hospital and medical services. It doesn’t cover outpatient prescription drugs at the pharmacy. You need a separate Part D plan for that.
Do I need Part D if I don’t take any medications?
You don’t legally have to enroll, but skipping it when you’re first eligible can result in a permanent late enrollment penalty that gets added to your premium later. A low-cost plan in the $15 to $20 per month range protects you from that penalty while you’re relatively healthy and not using much drug coverage.
Does Medicare Advantage replace both Medigap and Part D?
Usually, yes, in the sense that most Medicare Advantage plans (called MAPD plans) include drug coverage and limit your out-of-pocket costs. But you can’t have both Medicare Advantage and a Medigap plan. They’re incompatible. If you’re on Medicare Advantage with drug coverage included, you typically don’t need a separate Part D plan.
What’s the maximum I’d pay out of pocket for drugs under Part D in 2026?
Starting in 2025 and continuing in 2026, the annual out-of-pocket cap for Part D drug costs is $2,000. Before this change, people on expensive specialty medications could face much higher costs. The $2,000 cap is a significant improvement, especially for anyone managing a condition that requires high-cost drugs.
