When Can I Change My Medigap Plan in California?

If you have a Medicare Supplement (Medigap) policy in California, you are not locked into it forever. But the rules for switching are different from the rules for Medicare Advantage and Part D — and knowing which window you are in makes a real difference in whether a carrier can turn you down for health reasons.

Here is a plain-English guide to the times you can change your Medigap plan in California, and what to watch for with each one.

The short answer

There are four main situations when you can change a Medigap plan in California:

1. Your one-time Medigap Open Enrollment Period — the 6 months after you first enroll in Medicare Part B at 65 or older.
2. The California Birthday Rule — an annual window, beginning on your birthday, to move to a plan with equal or lesser benefits without medical underwriting.
3. A guaranteed-issue right — specific situations (like losing other coverage) that let you buy certain plans without underwriting.
4. Any other time — you can apply to switch whenever you want, but outside a protected window the carrier can use medical underwriting and may decline you.

One important point up front: the Annual Enrollment Period (October 15 – December 7) is for Medicare Advantage and Part D. It is not a window for changing Medigap plans. This is one of the most common points of confusion.

1. Your 6-month Medigap Open Enrollment Period

Your Medigap Open Enrollment Period starts the first month you are both 65 or older and enrolled in Medicare Part B. It lasts 6 months.

During this one-time window, you have the strongest rights you will ever have in the Medigap market. A carrier must sell you any Medigap policy it offers, cannot charge you more because of your health, and cannot make you wait for coverage of most pre-existing conditions. If you are shopping for or switching a Medigap plan during these 6 months, health questions generally do not apply.

Because this window does not come back, many people treat it as the moment to get the plan they really want. If you missed it or your situation has changed since, the next two options below are how Californians most often make a change later.

2. The California Birthday Rule

California is one of a handful of states with a "Birthday Rule" for Medigap. It gives existing Medigap policyholders an annual opportunity to switch plans without going through medical underwriting.

Here is how it works in practice:

• The window begins on your birthday each year. California law requires the window to last at least 30 days; in practice most carriers apply a 60-day window.
• You can move to any Medigap plan with equal or lesser benefits — for example, from one Plan G to another company's Plan G, or from Plan G to a plan with fewer benefits.
• No medical underwriting. The carrier cannot decline you or raise your price based on your health history during this window.
• It applies to people who already have a Medigap policy, including some people under 65 on Medicare due to disability.

The Birthday Rule is the reason a lot of Californians are able to shop their Medigap coverage once a year — often to find comparable benefits at a different price — even if their health has changed since they first enrolled. Because the details and timing matter, we cover them in depth in our full guide: California Birthday Rule for Medigap.

3. Guaranteed-issue rights

Separate from the Birthday Rule, federal law creates guaranteed-issue rights in certain situations. When one of these applies, carriers must sell you specific Medigap plans without underwriting, usually within a limited time (often 63 days from when your other coverage ends).

Common examples include:

• A Medicare Advantage plan you joined leaves Medicare or stops serving your area.
• You move out of your plan's service area.
• Your employer or union retiree coverage ends.
• You joined a Medicare Advantage plan when you first turned 65 and want to switch back to Original Medicare and Medigap within your first 12 months (a "trial right").

The plans available to you and the deadlines depend on which situation applies. If you think one of these fits you, it is worth confirming the specific right and timeline before your window closes.

4. Any other time (with medical underwriting)

Outside of the windows above, you can still apply to change your Medigap plan at any point in the year. The difference is that the carrier can ask health questions and use medical underwriting to decide whether to accept you and at what price. Depending on your health history, you may be approved, charged more, or declined.

This is why timing matters so much with Medigap. If you are in good health, applying anytime may work fine. If you have conditions that could affect underwriting, lining your change up with your Birthday Rule window or a guaranteed-issue right is usually the safer path.

How this is different from Medicare Advantage

If you are on a Medicare Advantage plan instead of Medigap, the change rules are completely different — Advantage and Part D changes happen mainly during the Annual Enrollment Period (Oct 15 – Dec 7) and, for current Advantage members, the Medicare Advantage Open Enrollment Period (Jan 1 – Mar 31). Moving from Medicare Advantage to Medigap has its own considerations, including underwriting — our guide to switching from Medicare Advantage to Medigap in California walks through it step by step. And if you are weighing the two approaches, see Medicare Advantage vs. Medicare Supplement (Medigap).

Frequently asked questions

Can I change my Medigap plan during the Annual Enrollment Period (Oct 15 – Dec 7)?

Not specifically. That window is for Medicare Advantage and Part D. Medigap changes in California run on the Medigap Open Enrollment Period, the Birthday Rule, guaranteed-issue rights, or year-round with underwriting.

Does the California Birthday Rule let me upgrade to a plan with more benefits?

No. The Birthday Rule lets you switch to a plan with equal or lesser benefits without underwriting. Moving to a plan with richer benefits would generally require medical underwriting outside a protected window.

How long is the California Birthday Rule window?

It begins on your birthday. State law requires at least 30 days, and most carriers apply a 60-day window. Confirm the exact dates with the carrier you are considering.

Can I be turned down when switching Medigap plans?

During your 6-month Medigap Open Enrollment, the Birthday Rule window, or a guaranteed-issue situation, no. Outside those windows, a carrier can use medical underwriting and may decline you or charge more.

Will my premium change if I switch?

Premiums vary by carrier, plan, age, and area, and they can change over time. A different company's version of the same plan letter covers the same standardized benefits but may be priced differently. Confirm current pricing directly with each carrier.

I'm under 65 and on Medicare — do these rules apply to me?

Some do. California extends certain Medigap protections to people under 65 on Medicare, and the Birthday Rule can apply to existing policyholders. The specifics depend on your situation, so it is worth reviewing before you apply.

Sources & official references

• Medicare.gov — Switching Medigap policies
• California Insurance Code § 10192.11 — annual open enrollment (birthday rule)
• California Department of Insurance — Medicare Supplement insurance guide
• California Health Advocates (HICAP) — Medigap counseling

This is a non-government resource and is not affiliated with or endorsed by Medicare.gov or the federal Medicare program. An independent broker may not offer every plan available in your area. For all of your options, contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Assistance Program (SHIP) — in California, HICAP. Last reviewed: July 2026. Medicare rules and figures reflect 2026 and can change; confirm current details at Medicare.gov.