Personal Finance & Estate › Medicare, Medi-Cal & long-term care › Medicare (federal health insurance at 65+)
Medigap (Medicare Supplement) & CA birthday rule
Standardized 1992· Insurance type
Depends on youExperts differ; the right answer depends on your situation.
Private insurance that pays most of Original Medicare's deductibles and 20% coinsurance, plus California's yearly 'birthday rule' for switching plans.
See it on the Personal Finance & Estate map →How it works
Plans are standardized by letter, so Plan G is identical across insurers; only price and service differ. Plan G now leads, since Plans C and F closed to people new to Medicare in 2020. It works with any doctor who takes Medicare but has no drug coverage, so add Part D. Buy in your 6-month Medigap open enrollment after Part B starts, when insurers can't refuse you. California's birthday rule then allows a yearly switch to equal or lesser coverage, no health questions.
Why it matters for you
Depends on you: it costs more each month but makes medical bills nearly predictable and keeps doctor choice wide, which matters most with chronic illness or travel.
Rules, limits and sources (2026)
Standardized under a 1990 federal budget law, effective 1992; California's birthday rule, set by state insurance law, was widened from 30 to 60 days after your birthday in 2020.
Watch out for
Premiums rise with age and claims; insurers argue California's birthday rule raises everyone's rates, while consumer groups say it keeps prices competitive.
Connections (2)
▸Medigap (Medicare Supplement) & CA birthday rule fills cost gaps in Medicare (federal health insurance at 65+)Standard practice
How they connect
Original Medicare leaves deductibles and an uncapped 20% coinsurance. Medigap is a private policy that pays those leftovers after Medicare pays its share; Medicare approves the claim first, then Medigap follows automatically. It works only with Original Medicare: insurers can't sell it to someone in a Medicare Advantage plan unless they are switching back.
When it applies
Supplemental policies date to Medicare's start in 1966; a 1990 federal budget law standardized them into lettered plans from 1992.
How sure?
Social Security Act Sec. 1882 governs Medigap; CMS's 'Choosing a Medigap Policy' guide lists the standardized plans.
Watch out for
Federal law guarantees Medigap access mainly at 65; whether more states should require year-round access, as New York does, is debated.
▸Medicare Advantage (Part C) competes with Medigap (Medicare Supplement) & CA birthday ruleDepends on you
How they connect
At 65 most people pick one path: Original Medicare plus Medigap and Part D (higher premiums, few bills, any doctor) or Medicare Advantage (low premiums, copays up to a yearly cap, networks). You can't combine them. Moving from Advantage to Medigap later usually means health questions, except under a 12-month trial right or special situations.
When it applies
The choice comes in the 6-month Medigap window at 65 and each October 15–December 7 open enrollment; HICAP counsels Californians free.
How sure?
Social Security Act Sec. 1882(s) on guaranteed issue and trial rights; CMS's 'Medicare & You' handbook compares the two paths.
Watch out for
Studies disagree on which path yields better health outcomes; some find sicker enrollees leave Advantage plans more often.