Medicare enrollment windows, deadlines, and penalties
Three windows, two penalties, one rule about when coverage starts. Get the dates right and Medicare is boring. Get one wrong and the cost follows you for the rest of your life.
Initial Enrollment Period
7 months: the 3 months before your birthday month, the month itself, and the 3 after. Born on the 1st? Everything shifts one month earlier.
Special Enrollment Period
8 months, starting the month after current-employment coverage (20+ employer) ends. Available any time while that coverage continues.
General Enrollment Period
January 1 to March 31 every year, for people who missed both. Coverage starts the first of the month after you sign up. Penalties apply.
When coverage actually starts
Since 2023 the start rule is simple: enroll before your birthday month and Part B begins on the first of that month; enroll during or after it and Part B begins the first of the month after you enroll. The old rule that delayed coverage by up to three months is gone. The practical advice is unchanged: apply in the first month of your window.
Born on the first of the month? Medicare treats you as turning 65 the month before, so a June 1 birthday means May eligibility and a February-to-August window. Our enrollment window calculator handles that case.
The two penalties
Part B: 10% per year, for life
For every full 12-month period you could have had Part B and did not, 10% is added to the standard premium ($202.90 in 2026) for as long as you have Part B. Two years late is $40.58 a month and about $9,739 over twenty years at today’s premium; it grows as premiums grow. Months covered by a current employer plan (20+ employees) are excluded.
Part B penalty calculator →Part D: 1% per month, for life
After your Initial Enrollment Period, a gap of 63 or more days without creditable drug coverage starts the clock. Each uncovered month adds 1% of the national base premium ($38.99 in 2026), rounded to the dime: 14 months is $5.50 a month. Employer drug coverage counts if HR confirms it is creditable.
Part D penalty calculator →The third window people forget: Medigap
Your six-month Medigap open enrollment starts the month Part B takes effect at 65 or older. During it, any Medigap insurer in Utah must sell you any plan it offers at the standard rate, regardless of health history. After it, Utah allows medical underwriting outside a short list of guaranteed-issue situations. If you delayed Part B for work, the window starts when Part B finally starts, so the two decisions travel together.
Applying: what to have ready
Apply at ssa.gov/medicare (about ten minutes) or by calling 1-800-772-1213. Have your Social Security number, birth certificate or passport details, and, if you are enrolling after 65 because of employer coverage, form CMS-L564 completed by the employer plus CMS-40B. If you already receive Social Security or Railroad Retirement benefits, you are enrolled automatically and your card arrives about three months before your birthday; you may decline Part B by following the instructions on the card, but not Part A.
Sources
- Medicare.gov, "When does Medicare coverage start?"
- Medicare.gov, "Avoid late enrollment penalties"
- Medicare.gov, "How much does Medicare drug coverage cost?" (2026 national base beneficiary premium $38.99)
- Medicare.gov, "When can I buy a Medigap policy?"
- Social Security, "Sign up for Medicare"
- Utah Insurance Department, Medicare / Medigap / Medicare Advantage
Deadline questions, answered
Is it mandatory to sign up for Medicare at 65?
No law forces you. But if you have no current-employment coverage from a 20+ employer, the Part B penalty starts accruing when your 7-month Initial Enrollment Period ends, and marketplace subsidies end once you are eligible for premium-free Part A.
How many months in advance should I sign up?
Three. Enroll in the three months before your birthday month and coverage starts on the first day of that month. Sign up during or after the birthday month and coverage starts the first of the following month.
What happens if I don’t sign up for Medicare at 65?
Without a qualifying employer plan: the Part B penalty (10% per full year, for life), a possible Part D penalty (1% per month), a possible coverage gap until the next General Enrollment Period, and a lost Medigap open enrollment window.
How long does it take to get Medicare after applying?
If you already receive Social Security, enrollment is automatic and your card arrives about three months before your 65th birthday. If you apply online at ssa.gov, most decisions arrive within a few weeks; apply early in your window.
Do the math
Enrollment window calculator
Your windows from your birthday, including the born-on-the-1st rule.
Open the tool →
Talk it through before you decide
Bring your birth date, your work situation, and last year’s tax return. Leave knowing your enrollment window, what Medicare will cost you, and whether the income surcharge applies.
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