Your Open Enrollment Window Is the Only Time You’re Guaranteed Coverage
The best time to enroll in a Medicare supplement plan is during your Medigap Open Enrollment Period, which starts the month you turn 65 and are enrolled in Medicare Part B. You get exactly six months. That window closes whether you use it or not, and once it’s gone, most states won’t give it back.
Here’s why that window matters so much: during those six months, insurance companies are legally required to sell you any Medigap plan they offer at their standard rates. They can’t ask about your health. They can’t turn you down for a pre-existing condition. They can’t charge you more because you had cancer three years ago or because you take five medications. That’s called guaranteed issue, and it only exists automatically during this specific window.
Outside of open enrollment, insurers in most states can run you through medical underwriting. That means they ask detailed questions about your health history, and they can decline your application entirely or charge you a higher premium based on what they find. I’ve seen people in their late 60s get flat-out rejected because of conditions as common as well-managed diabetes or a history of sleep apnea. It’s not a theoretical risk. It happens constantly.
So if you’re approaching 65, the single most actionable thing I can tell you is: don’t wait, and don’t assume you’ll be able to get coverage later. Enroll during your open enrollment window, even if you feel perfectly healthy right now.
What “Turning 65” Actually Means for Your Timeline
Your Medigap Open Enrollment Period starts on the first day of the month you turn 65, provided you’re already enrolled in Medicare Part B. That second part trips people up more than anything else I’ve seen.
If you delayed Part B enrollment because you had employer coverage, your six-month Medigap window doesn’t start at 65. It starts when you actually enroll in Part B. So a 68-year-old who just retired and signed up for Part B this month gets a full six-month Medigap window starting now. Age 65 isn’t the trigger. Part B enrollment is.
That’s genuinely good news for people who work past 65. You’re not penalized just for delaying. But here’s the catch: you need to enroll in Part B promptly when your employer coverage ends. If you let Part B enrollment lapse or miss a deadline, you could end up in a gap situation where you’ve also lost your Medigap guaranteed issue rights, and now you’re trying to get coverage in your late 60s with a health history that makes underwriting risky.
One more thing worth knowing: if your birthday is on the first of the month, Medicare considers your coverage to begin on the first of the prior month. It’s a quirk in how Social Security calculates benefit start dates. If that applies to you, verify your exact Part B start date with Social Security directly before assuming your Medigap window dates.
The Timing Mistake That Costs People Thousands
I want to be direct about the most common mistake I see: people wait until they actually get sick or have a major procedure scheduled, and then they try to buy a Medigap plan. By that point, they’re either denied outright or they’re stuck with whatever options are available to them at unfavorable rates.
The misconception driving this mistake is that Medigap works like a product you can shop for when you need it. It doesn’t. It’s closer to life insurance in how it’s underwritten outside of protected windows. You can’t wait until you have a heart condition to buy coverage that helps pay for cardiac care. The insurer knows exactly what you’re going to use it for, and they’ll decline you.
A related mistake is assuming that Medicare Advantage is a fine backup plan if you can’t get Medigap. In the short term, it might be. But Medicare Advantage plans come with networks, prior authorizations, and cost-sharing structures that can get expensive fast when you’re dealing with serious illness. I’ve talked with people in their early 70s who ended up on Advantage plans after losing their Medigap window, racking up thousands in out-of-pocket costs during hospitalizations that a Plan G would have covered almost entirely.
The 2026 Part A deductible is $1,676 per benefit period. The 2026 Part B deductible is $257. Those aren’t numbers you want to face repeatedly in a bad health year without a supplement. Plan G covers both once you pay the Part B deductible yourself. That’s the whole point of having it.
When You Can Still Get Guaranteed Issue After Your Main Window
There are situations where federal law guarantees you the right to buy a Medigap plan even outside your initial open enrollment window. These are called Special Enrollment Periods or guaranteed issue rights, and it’s worth knowing when they apply.
The main scenarios where you’re protected include:
- Your Medicare Advantage plan is leaving your area or stopping operations
- You move out of your Medicare Advantage plan’s service area
- You had employer group health coverage that ends
- You enrolled in Medicare Advantage when you first became eligible and you want to switch back to Original Medicare within 12 months
- You lose Medicaid coverage you previously had
These rights are federal guarantees, but they’re narrow. They apply to specific plan types, and in most cases you’re limited to buying Plan A, B, C, F, K, or L from any insurer, or Plan D or G from certain insurers. You can’t always get any plan you want.
Some states give their residents broader protections. California, Connecticut, Maine, Massachusetts, Missouri, New York, and Washington have their own rules that provide more open enrollment opportunities or limit underwriting more strictly than federal law. If you live in one of these states, check your state-specific rules before assuming federal minimums are all you have.
How Premium Timing Affects Your Total Cost
Here’s something most articles don’t address clearly: when you enroll affects your premium, not just your eligibility. Medigap premiums are typically based on your age at enrollment. The younger you are when you lock in a plan, the lower your starting premium. That difference compounds over years of coverage.
Look at how premiums typically compare by age for a Plan G in Ohio:
| Age at Enrollment | Estimated Monthly Premium (Plan G, Ohio) | Estimated 10-Year Total Cost |
|---|---|---|
| 65 | $115 | $13,800+ |
| 67 | $135 | $16,200+ |
| 70 | $165 | $19,800+ |
| 72 | $190 | $22,800+ |
These are illustrative figures based on typical insurer pricing in Ohio as of 2026. Actual premiums vary by insurer and county. But the pattern holds everywhere: waiting costs you more per month, and that gap adds up quickly.
That said, I want to give honest advice for people who are still working with good employer coverage past 65. If your employer plan has low cost-sharing and solid coverage, there’s a real argument for staying on it and waiting to start Medigap when you actually retire. You’re not losing your Medigap window as long as you have creditable coverage through your employer and you enroll in Part B when that ends. Just don’t let it drag on past your Part B enrollment window and into a situation where you’re trying to get underwritten at 74 with a complicated health history.
Bottom Line
For most people, the best time to enroll in a Medicare supplement plan is the month you turn 65 and enroll in Part B, and you should treat that six-month window like the limited resource it is. If you’re still working with good employer coverage, enroll in Medigap as soon as you retire and sign up for Part B. Don’t wait to see how your health goes, because by the time you know you need coverage, it may be too late to get it at a standard rate, or at all.
Frequently Asked Questions
Can I be denied Medigap coverage if I apply during my open enrollment period?
No. During your six-month Medigap Open Enrollment Period, insurers are legally required to sell you any plan they offer at standard rates, regardless of your health history. Denials and medical underwriting only apply if you apply outside of that window without a qualifying special enrollment situation.
What happens if I miss my Medigap open enrollment window?
In most states, you’ll have to go through medical underwriting when you apply. Insurers can reject your application, charge you higher premiums, or impose waiting periods on pre-existing conditions. A handful of states have stronger protections, so check your state’s specific rules if you’ve already missed your window.
Is there a penalty for enrolling in Medigap late, like there is for Part B?
No, there’s no federal late-enrollment penalty for Medigap the way there is for Part B or Part D. But the practical consequence is that you lose guaranteed issue protections, which can be far more costly than a percentage-based penalty. You might not be able to get the plan you want at all.
If I’m 68 and just retired, is it too late to get a Medigap plan?
Not necessarily. If you’re enrolling in Part B now because you just left employer coverage, your Medigap open enrollment window opens now and runs for six months. You’re protected under guaranteed issue rules for that window regardless of your age. Get your Part B enrollment confirmed and then shop for a supplement plan right away.
