Medicare is the federal health insurance program for people 65 and older — and for certain younger individuals with disabilities or end-stage renal disease. Understanding enrollment rules before you turn 65 can prevent costly, permanent premium penalties.
The four parts of Medicare
Medicare has four parts, each covering a different category of care:
- Part A (Hospital Insurance) — inpatient hospital stays, skilled nursing facility care, hospice, and some home health care
- Part B (Medical Insurance) — doctor visits, outpatient services, preventive care, and durable medical equipment
- Part C (Medicare Advantage) — a private-insurer alternative to Original Medicare; each plan must cover at least the same benefits and most bundle Part D coverage plus extras like dental and vision
- Part D (Prescription Drug Coverage) — standalone prescription drug plans that pair with Original Medicare
Most people start with Original Medicare (Parts A and B) and then decide separately whether to add a Medicare Advantage plan or pair Original Medicare with a Medigap supplement and standalone Part D drug plan. For a primer on Medigap plan types, see What Is a Medicare Supplement (Medigap) Plan?.
Part A: usually free
Premium-free Part A is available to anyone who — or whose spouse — worked and paid Medicare taxes for at least 40 quarters (10 years) in the U.S. Per Medicare.gov, the large majority of new enrollees at 65 qualify.
People who worked 30–39 quarters can still enroll in Part A but pay a reduced monthly premium; fewer than 30 quarters results in a higher rate. CMS publishes the current Part A premium amounts each fall for the following year.
Part A carries a per-benefit-period hospital deductible — $1,736 in 2026 — plus daily coinsurance for stays longer than 60 days. There is no annual cap on Part A deductibles because each "benefit period" resets 60 days after discharge.
Part B: $185/month in 2026
Part B is not free. The standard monthly premium is $185.00 in 2026, per the CMS 2026 Medicare Parts B Premiums and Deductibles fact sheet. The annual Part B deductible is $283. After the deductible, Original Medicare pays 80% of most approved outpatient services; you pay the remaining 20% — with no annual out-of-pocket ceiling under Original Medicare alone.
Higher-income beneficiaries pay an Income-Related Monthly Adjustment Amount (IRMAA): an additional monthly premium based on the modified adjusted gross income reported on your tax return two years prior. CMS adjusts IRMAA thresholds annually — verify current brackets directly with CMS. If your income dropped significantly since the base year (retirement is a common trigger), you can request a new initial determination using a more recent tax return.
Your Initial Enrollment Period — the primary window
The Initial Enrollment Period (IEP) is a 7-month window:
- The 3 months before the month you turn 65
- The month you turn 65
- The 3 months after the month you turn 65
Enrolling during the 3 months before your birthday month gives you coverage starting the month you turn 65. Enrolling in your birthday month or later delays your coverage start date by 1–3 months. Per SSA.gov, you can apply for Medicare online through the Social Security Administration even if you have not yet started claiming Social Security retirement benefits.
When you can delay without penalty
If you are covered by active employer-sponsored insurance from your own current job or a spouse's current job at 65, you can delay Part B without facing the late-enrollment penalty. When that active coverage ends, you qualify for a Special Enrollment Period (SEP): an 8-month window beginning the month after your employment or employer coverage ends, whichever comes first.
Two rules that trip up many people:
- COBRA is not active employer coverage. Once you leave employment and move to COBRA continuation, the 8-month SEP clock starts immediately — you cannot wait out the full COBRA period without triggering a late penalty.
- Retiree health insurance is not active employer coverage. Coverage from a former employer's retiree benefit plan also does not preserve your SEP rights.
For self-employed business owners managing their own health coverage as they approach 65, see Health Insurance for Self-Employed Business Owners in 2026 for how individual-market and ACA plans interact with Medicare timing.
The General Enrollment Period
If you miss both the IEP and a valid SEP, you can still enroll during the General Enrollment Period (GEP): January 1 through March 31 of each year. Coverage under GEP starts July 1.
The trade-off: enrolling via GEP typically triggers the late-enrollment penalty unless you have a valid exception.
Late enrollment penalties — permanent premium increases
Part B late penalty: 10% is added to the standard monthly Part B premium for each full 12-month period you were eligible but did not enroll. This surcharge is permanent — it applies for as long as you have Part B. A 2-year delay adds 20% to every monthly premium for life; a 3-year delay adds 30%. On a $185/month base premium, that 30% penalty amounts to an extra $55.50 every month, indefinitely.
Part D late penalty: 1% of the national base beneficiary premium multiplied by the number of months you went without creditable prescription drug coverage. This also applies permanently and is recalculated each year as the base premium changes.
Part A penalty (for those who owe premiums): If you don't qualify for premium-free Part A and don't enroll when first eligible, your Part A premium increases by 10% for twice the number of years you delayed.
IRMAA — higher-income surcharges
IRMAA applies to Part B and Part D for beneficiaries whose modified adjusted gross income exceeds set thresholds, using income from two years prior. Because the surcharge is calculated from a prior year's income, a significant income drop — retirement, sale of a business, or a one-time capital event — can create an IRMAA bill based on income you no longer have. You can file for a Life-Changing Event appeal with SSA to use a more recent income estimate.
Medicare enrollment and Social Security timing
Medicare and Social Security are independent programs. If you are already receiving Social Security when you turn 65, per SSA.gov you are automatically enrolled in Part A and Part B — your Medicare card arrives approximately 3 months before your 65th birthday. If you have not started Social Security, you must actively sign up for Medicare.
When you claim Social Security — at 62, at Full Retirement Age (67 for those born in 1960 or later), or at 70 — does not affect your Medicare enrollment window. For a breakdown of that separate decision, see When to Claim Social Security: Age 62, Full Retirement Age, or 70?.
This content is educational and does not constitute health insurance or financial planning advice. Medicare premiums, enrollment periods, and penalty rules are subject to annual change. Verify current figures at medicare.gov and cms.gov before making enrollment decisions.
