Enrolling in Medicare: timing, methods, and the military-specific rules

Medicare enrollment is the single most important administrative step in your transition. Get it right and TRICARE For Life activates the same day Part B is effective. Get it wrong and you can face a permanent premium penalty, a gap in coverage, and loss of TFL.

This lesson walks through who enrolls automatically, who must enroll actively, when to do it, and how.

Are you enrolled automatically?

You are auto-enrolled in Parts A and B if any of these are true on the month you turn 65:

• You already receive Social Security retirement benefits.
• You already receive Railroad Retirement Board benefits.
• You already receive Social Security Disability Insurance (SSDI) and have for 24+ months.

SSA mails your red, white, and blue Medicare card about 3 months before your 65th birthday. Part A is free; Part B carries a premium that will be automatically deducted from your Social Security check.

You can decline Part B by returning the card with the form on the back — but for TRICARE For Life beneficiaries, declining Part B ends your TRICARE eligibility.

If you are NOT auto-enrolled

If you are not yet collecting Social Security at 65, you must actively sign up. There are three ways:

Online (fastest, recommended)

Go to ssa.gov/medicare/sign-up. The application takes 10–15 minutes. You will need your Social Security number, your DD-214 (helpful for verification), and direct-deposit info for any future SSA benefits.

By phone

Call Social Security at 1-800-772-1213 (TTY 1-800-325-0778), Monday–Friday, 8 a.m. – 7 p.m. local time.

In person

Visit your local Social Security office. Appointments are strongly recommended — schedule online or by phone.

The three enrollment windows

The IEP month-by-month

Your IEP is exactly 7 months long. The earlier in the IEP you apply, the earlier Part B becomes effective.

• Apply in months 1–3 (the three months before your birthday month): Part B starts the first day of your birthday month.
• Apply in month 4 (your birthday month): Part B starts the first day of the following month.
• Apply in months 5–7 (the three months after): Part B starts the first day of the month after you apply.

For TRICARE For Life beneficiaries, apply in the first three months of your IEP. This guarantees Part B (and therefore TFL) is active the day TRICARE Prime/Select ends.

Critical timing rule: TRICARE Prime and TRICARE Select end at midnight on the last day of the month before you turn 65. Part B must be active by the first of your 65th-birthday month, or you will have a coverage gap.

What about Part A only?

Part A is premium-free for almost all retirees because you (or your spouse) paid Medicare taxes for at least 40 quarters. You should accept Part A.

But you cannot keep TRICARE For Life with Part A alone. TFL requires both Part A and Part B. Declining Part B is the same as declining TFL.

What about Part D?

Do not enroll in Medicare Part D. TRICARE Pharmacy (administered by Express Scripts) is "creditable" prescription drug coverage — better than most Part D plans and with no premium. Enrolling in Part D can disrupt your TRICARE Pharmacy benefits and is unnecessary.

What if I'm still working?

If you (or your spouse) have active, employer-sponsored group health coverage at age 65, you may delay Part B without penalty and enroll later under a Special Enrollment Period when that coverage ends. In this case, TRICARE Prime/Select also continues.

However, the moment that employer coverage ends, you have 8 months to enroll in Part B (and TFL activates on Part B's effective date).

Common enrollment mistakes

• Waiting for a letter from TRICARE. DHA sends reminders, but enrollment is your responsibility.
• Assuming spouse will be enrolled with you. Each spouse enrolls based on their own birthday.
• Declining Part B to save money. You lose TFL entirely — a far costlier mistake.
• Applying in month 4 or later of your IEP. You'll have at least a one-month gap.
• Enrolling in Part D "just in case." Unnecessary and may interfere with TRICARE Pharmacy.

Continue learning

— suggested by the knowledge graph

Lessons

• What is Medicare? A complete overview for retired militaryA plain-English, handbook-grounded overview of the federal health insurance program for people 65 and older, written specifically for retired service members and their families.
• Common mistakes retired military make at 65 — and how to avoid themThe most expensive errors retired service members and spouses make during the Medicare and TFL transition, and the simple fixes for each.
• What is TRICARE For Life? The complete guide for retired militaryThe Medicare-wraparound benefit you earned through service — what it covers, who qualifies, what it costs, and how it activates.
• Frequently asked questions about Medicare and TRICARE For LifeA quick-reference summary of the questions retired service members and spouses ask most often — with citations to the official source.

Encyclopedia

• Medicare Part AThe hospital insurance side of Original Medicare — covers inpatient stays, skilled nursing, hospice, and some home health.
• Medicare Part BThe medical insurance side of Original Medicare — covers doctor visits, outpatient care, preventive services, and durable medical equipment.
• Medicare Part DMedicare's optional prescription drug coverage — almost always unnecessary if you have TRICARE For Life.
• TRICARE For Life (TFL)The wraparound secondary health coverage for Medicare-eligible military retirees, spouses, and survivors — no premium, no enrollment fee.
• DEERSThe DoD's master database that determines who is eligible for TRICARE — including TRICARE For Life.
• milConnectThe DoD self-service web portal where retirees verify and update DEERS, view TRICARE coverage, and request ID cards.
• Initial Enrollment Period (IEP)The 7-month window around your 65th birthday when you first sign up for Medicare Parts A and B without penalty.
• General Enrollment Period (GEP)The January 1 – March 31 window each year when you can sign up for Medicare if you missed your IEP and don't qualify for an SEP.
• Special Enrollment Period (SEP)An enrollment window triggered by qualifying life events — TRICARE and VA care do NOT trigger one.
• TRICARE Pharmacy ProgramThe DoD prescription drug benefit administered by Express Scripts — your drug coverage if you have TFL.

FAQs

• I'm turning 65. What should I do first?About 3 months before your 65th birthday, sign up for Medicare Parts A and B at SSA.gov. TRICARE For Life activates automatically once both are effective and DEERS is current.
• Do I need to cancel TRICARE Prime or Select when I turn 65?No. Prime and Select end automatically when you become Medicare-eligible. You don't have to take any action — and your Prime enrollment fee withholding stops.
• I missed my Medicare enrollment window. Now what?Use the General Enrollment Period (Jan 1 – Mar 31). You'll likely owe a Part B late penalty for life, and you'll have no TFL until Part B is effective.
• Do I need Medicare Part A if I have TRICARE?Yes. TFL requires Part A and Part B. Part A is typically premium-free if you or your spouse worked 40+ quarters paying Medicare taxes.
• How long does Medicare enrollment take to process?Most online applications are approved in 1–3 weeks. SSA mails the Medicare card within about 30 days of approval.
• What is the 5-star Special Enrollment Period?A one-time-per-year chance (Dec 8 – Nov 30) to switch into a 5-star-rated Medicare Advantage or Part D plan in your area, outside the normal enrollment windows.