Reviewed for accuracy by Lauri Middleton, RN, MSN, licensed Medicare agentReviewed for clarity by Karen OrillaMeet our reviewers →
The rules we use
Every date and consequence on the site traces back to one of these cards. Each has its official source, when it took effect and when we last checked it.
It starts three months before the month you turn 65, includes that month, and ends three months after it. If your birthday is on the 1st, the whole window moves one month earlier.
Source: Medicare.gov — When does Medicare coverage start? · In effect since 2023-01-01 · Last checked 2026-09-06
Sign up in the three months before your birthday month and Part B starts on the first day of that month. Sign up in your birthday month or the three months after, and it starts on the first day of the month after you sign up. The older two-to-three-month delays ended in 2023.
Source: Medicare.gov — When does Medicare coverage start? · In effect since 2023-01-01 · Last checked 2026-09-06
After your first enrollment period, a gap of 63 consecutive days or more without Part D or other creditable drug coverage can lead to a late penalty. People who get Extra Help do not pay this penalty.
Source: Medicare.gov — Part D costs and the late enrollment penalty · In effect since 2006-01-01 · Last checked 2026-09-06
It starts the first month you are 65 or older and enrolled in Part B. During those six months a company must sell you any Medigap policy it offers, at the same price as someone in good health. Outside it, rights vary by state.
Source: Medicare.gov — Ready to buy Medigap · In effect since 1992-01-01 · Last checked 2026-09-06
If you or your spouse are still working and you have health coverage from that job, you can sign up for Part B later without a penalty. The window is eight months, starting the month after the job or the coverage ends — whichever comes first. COBRA and retiree coverage do not count as coverage from a current job.
Source: Medicare.gov — Working past 65 · In effect since 2023-01-01 · Last checked 2026-09-06
The Part D window after losing job-based drug coverage is shorter than the Part B one: two months after the coverage ends. Ask the benefits office for a letter saying whether the drug coverage was creditable.
Source: Medicare.gov — Special Enrollment Periods · In effect since 2006-01-01 · Last checked 2026-09-06
With 20 or more employees, the job plan pays first and Medicare second, so delaying Part B is usually safe while that coverage lasts. With fewer than 20, Medicare pays first — and if you have not signed up, the job plan may pay very little.
Source: Medicare.gov — Working past 65 · In effect since 1986-01-01 · Last checked 2026-09-06
Part A can be backdated up to six months when you sign up after 65. Contributions made for any month you have Part A are not allowed, so the safe stop is six months before the month you plan to apply — but never earlier than your eligibility month.
Source: Medicare.gov — Working past 65 · IRS Publication 969 · In effect since 2004-01-01 · Last checked 2026-09-06
If the first window closed and no special window applies, you can sign up for Part B between January 1 and March 31 each year. Coverage starts the first day of the month after you sign up.
Source: Medicare.gov — When does Medicare coverage start? · In effect since 2023-01-01 · Last checked 2026-09-06
For every full 12-month period you could have had Part B but did not — and were not covered by a current job — the monthly premium goes up by 10 %. It stays that way for as long as you have Part B.
Source: Medicare.gov — Avoid late enrollment penalties · In effect since 1966-01-01 · Last checked 2026-09-06
When a Part D penalty applies, Medicare counts full uncovered months at 1% of the national base premium and rounds the penalty to the nearest 10 cents. It generally lasts while you have Part D; Extra Help is an exception.
Source: Medicare.gov — Part D costs and the late enrollment penalty · In effect since 2006-01-01 · Last checked 2026-09-06
After the first year, this is when anyone with Medicare can join, switch or drop a Medicare Advantage or Part D plan for the following January.
Source: Medicare.gov — Joining a plan · In effect since 2011-01-01 · Last checked 2026-09-06
Someone already in a Medicare Advantage plan can switch to another one, or go back to Original Medicare (and add a Part D plan), between January 1 and March 31. Only one change in that window.
Source: Medicare.gov — Joining a plan · In effect since 2019-01-01 · Last checked 2026-09-06
Extra Help lowers Part D costs and is applied for through Social Security. Medicare Savings Programs help with Part B premiums and sometimes more, and are applied for through the state Medicaid office (Medi-Cal in California). Both look at income and resources; this site does not screen for them.
Source: SSA — Extra Help · Medicare.gov — Medicare Savings Programs · In effect since 2006-01-01 · Last checked 2026-09-06
Part B and Part D premiums are set from the tax return two years back. If income dropped because of retirement, a death, divorce or a lost pension, Social Security can use the current year instead — form SSA-44.
Source: SSA — Medicare premiums: rules for higher-income beneficiaries · In effect since 2007-01-01 · Last checked 2026-09-06
Original Medicare gives 120 days from the notice to ask for a redetermination; Medicare Advantage and Part D plans have their own timelines, printed on the denial. Free HICAP counselors help with appeals.
Source: Medicare.gov — Appeals · In effect since 2005-01-01 · Last checked 2026-09-06
