Medicare Supplement
Medigap: how it works, and the window that closes
Figures on this page checked . Medicare and marketplace numbers reset every year — if you are reading this long after that date, call and we will tell you what moved.
It works with Medicare, it doesn’t replace it
You keep Original Medicare. Medicare pays first, your Medigap policy helps pay the deductibles and coinsurance left behind, and you pay a monthly premium for that. No network applies: any provider in the country who accepts Medicare accepts your Medigap policy, and you never need a referral.
Medigap does not include drug coverage, so you will need to enroll in a standalone Part D plan as well.
The plan letters are standardized by law
A Plan G from one carrier covers exactly what a Plan G from any other carrier covers. The benefits are set federally, so carriers compete on price, service, and how much they raise rates later — not on what the policy does.
So the only difference between two Plan G quotes is the price and the carrier charging it. A much cheaper one is not a better one — same coverage, different pricing history. Ask about the history.
Most people compare Plan G and Plan N. Two get overlooked: high-deductible G trades a much lower premium for a real deductible, and Plans K and L cap your year while leaving you a share along the way.
Plans C and F are closed to anyone who became eligible for Medicare on or after January 1, 2020. If you already have one you can keep it.
The six months that decide whether you can buy one
Your Medigap Open Enrollment Period runs six months from the month you are both 65 or older and enrolled in Part B. Inside it, carriers must sell you any policy they offer at their standard rate, no health questions asked.
What changes when it closes
Outside that window, Colorado allows carriers to use medical underwriting — they can ask about your health, charge more, or decline you. No annual do-over exists.
This is the asymmetry that makes the choice at 65 harder to reverse than it looks. Medicare Advantage asks no health questions; you can join one later. Coming back the other way may require answering health questions you could not answer today.
The doors that open on their own
Some situations put you back inside guaranteed issue after your six months have gone. They are events rather than dates — nothing on the calendar brings one round — and the two that come up most are your plan being canceled and you moving out of its service area.
Inside one of these, a carrier cannot decline you, cannot charge you more for your health history, and cannot refuse to cover a condition you already have. What you get is a defined list of plans rather than the whole shelf: Plan A, B, D, G — including high-deductible G — K or L, from any carrier, if you reached Medicare in 2020 or later. Plan N is not on it, which surprises people who had settled on Plan N.
Your plan ended it
6 months
Canceled, not renewed, or pulled out of your county. The clock runs from the day the coverage ends.
You ended it
63 days
And it opens 60 days before you leave, so you can be approved for the new policy before the old one stops.
The upright line is the day your old coverage ends.
Colorado sets both of these in the same regulation, and the shorter one is the number that gets quoted at everybody. If your plan was canceled and someone tells you the window has closed, check the date against six months before you believe it.
Keep the letter
If a plan writes to tell you it is ending, do not throw the letter away. Colorado requires that you have to send evidence of the termination date with the application — so the notice is not paperwork about the door, it is the proof the door is open. Photograph it and send us the photograph.
Two more open the door and both have a twelve-month clock on them. If Medicare Advantage was the first coverage you ever chose on Medicare and you leave within a year, you can buy any supplement policy from any carrier — no plan-letter list at all. And if you dropped a Medigap policy to try Advantage for the first time and come back within a year, you can have your old policy back from the same carrier if they still sell it.
Nothing arrives to remind you either clock is running. If you took an Advantage plan last autumn, the date to know is twelve months from when it started.
What Colorado does and doesn’t offer
Some states have a Medigap “birthday rule” — an annual window where you can switch to an equal or lesser plan without underwriting. Colorado is not one.
This matters because birthday-rule articles written for California or Oregon rank well and sound like general Medicare advice. They are not advice for you. If someone tells you that you can always switch later, ask them which state they mean.
Colorado does something many states do not, though, and it works in your favor if you reached Medicare through disability before 65: carriers here have to sell to you. Every policy they currently offer, during a six-month window that opens when your Part B starts rather than at 65.
Rates for under-65 policies can be higher, and then a second window opens at 65 — which is the moment to shop again. The under-65 rules are their own page.
Questions about Medigap
Can I switch Medigap plans later without answering health questions?
In Colorado, generally no. This state has no birthday rule and no annual guaranteed-issue window. Once your six-month window closes, a carrier can underwrite you.
Several specific situations do reopen the door: your plan being canceled or not renewed, it pulling out of your county, you moving out of its service area, a retiree plan that supplemented Medicare ending, your carrier failing, losing Medicaid, and a trial right in your first twelve months on Medicare Advantage. They are circumstances rather than a yearly opportunity, so ask before you assume one applies — and ask before you assume one has expired.
The window is six months when your plan ended it and 63 days when you did. Guides quote the 63 at everybody, which is how somebody gets told they are too late four months early.
What’s the difference between Plan G and Plan N?
Plan N has a lower premium and asks you to pay small copays for some office and emergency visits, plus the Part B deductible. Plan G covers everything except that deductible.
A third difference gets left out of most comparisons. A doctor who has not signed Medicare's participation agreement can bill you above what Medicare approves — up to 15% over, on the services the limit covers. Colorado's own Medigap regulation sets out what each plan does about that, and the two answers are opposite: on Plan G the policy pays 100% of it and you pay nothing, and on Plan N the policy pays nothing and you pay all of it.
Which wins depends on how often you see a doctor, whether your doctors take assignment, and whether you would rather pay steadily or occasionally. For someone with a chronic condition and frequent visits, Plan G often costs less in total despite the higher premium. We will run both against your year and your doctors.
One timing note: if a guaranteed-issue right is what gets you in the door, Plan N is not on the list of plans you are entitled to. Plan G is.
Why did Plan F disappear?
Federal law closed Plan F, and the high-deductible version, to anyone newly eligible for Medicare from January 1, 2020, because it covered the Part B deductible and Congress wanted beneficiaries to see some first-dollar cost.
If you were eligible before then you can still buy or keep one. The practical catch is that a closed plan takes in no new, younger members, which tends to push rate increases up over time. Watch it rather than panicking about it.