TRICARE to Medicare at 65: The Part B Window
TRICARE For Life requires Medicare Part A and Part B. Miss the Part B window and you face a permanent 10% per year penalty. Here is the timeline.
Every military retiree who turns 65 faces a deadline that no one at the retirement briefing emphasizes enough. Miss the Medicare Part B enrollment window and you lose TRICARE coverage. Not temporarily. Permanently, until you fix it, and even then the financial penalty follows you for life.
What Changes at 65?
For most of your military retirement, TRICARE Prime or TRICARE Select has been your primary health coverage. At 65, that ends. You transition to TRICARE For Life (TFL), which works differently. TFL is not a standalone plan. It is a Medicare supplement. It wraps around Medicare, picking up most of the costs that Medicare does not cover: copays, coinsurance, and certain services Medicare excludes.
But here is the critical requirement: TFL only works if you have both Medicare Part A and Medicare Part B. Part A alone is not enough.
The Part B Enrollment Timeline
Medicare Part A (hospital insurance) is automatic and free for most retirees who paid Medicare taxes for at least 40 quarters. You are enrolled automatically at 65.
Medicare Part B (medical insurance) is not automatic for TRICARE beneficiaries. You must actively enroll. The window is called the Initial Enrollment Period, and it spans seven months:
| Month Relative to 65th Birthday | Action Available |
|---|---|
| 3 months before | Enrollment opens |
| Birth month | Midpoint |
| 3 months after | Enrollment closes |
If your 65th birthday is October 15, your Initial Enrollment Period runs from July 1 through January 31 of the following year.
The 2026 standard Medicare Part B premium is $202.90 per month. Higher earners pay more through Income-Related Monthly Adjustment Amounts (IRMAA), which are based on modified adjusted gross income from two years prior.
What Happens If You Miss the Window?
Two things, both painful.
1. You lose TRICARE coverage. Without Part B, you are not eligible for TRICARE For Life. That means no TRICARE coverage of any kind after 65. You are on Medicare Part A alone, which covers hospital stays but not doctor visits, outpatient care, lab work, or most of the day-to-day medical expenses retirees face.
2. You pay a permanent premium penalty. The Medicare Part B late enrollment penalty adds 10% to your monthly premium for every full 12-month period you were eligible but did not enroll. This penalty never goes away. You pay it for as long as you have Part B.
Here is what the math looks like at the 2026 premium rate:
| Years Late | Penalty | Monthly Premium | Annual Cost vs. On-Time |
|---|---|---|---|
| On time | 0% | $202.90 | $0 |
| 1 year late | 10% | $223.19 | $243.48 extra/yr |
| 2 years late | 20% | $243.48 | $486.96 extra/yr |
| 3 years late | 30% | $263.77 | $730.44 extra/yr |
| 5 years late | 50% | $304.35 | $1,217.40 extra/yr |
And the base premium rises every year with healthcare inflation. The 2026 premium is $202.90, up from $185.00 in 2025. Your penalty percentage applies to whatever the current premium is, not what it was when you should have enrolled.
Over a 20-year retirement from 65 to 85, a two-year-late enrollment penalty costs roughly $9,739 in extra premiums, assuming 3% annual premium inflation.
Why Military Retirees Specifically Get Caught
The trap is that TRICARE works so well before 65 that many retirees assume it will continue. The transition is not optional. TRICARE Prime and TRICARE Select terminate at 65 for Medicare-eligible beneficiaries. There is no way to keep your pre-65 TRICARE plan.
Active-duty service members and their families are exempt from this transition while the member is on active duty. But once the member retires and reaches 65, the same rules apply.
Another common confusion: veterans who use the VA health system may assume that covers them. VA healthcare and TRICARE are separate programs. VA healthcare does not require Medicare Part B. But if you want TRICARE For Life as your supplement (and most military retirees do, because TFL covers dependents and has no enrollment fee beyond the Part B premium), you need Part B.
The General Enrollment Period Rescue (With Strings)
If you missed your Initial Enrollment Period, you can sign up during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage starts July 1 of that year. That means a gap of at least three months with no TRICARE and no Part B coverage.
During the gap, you are responsible for 100% of outpatient medical costs. A single ER visit or specialist consultation during those months can cost thousands.
IRMAA: The Hidden Cost for Higher Earners
Military retirees with substantial pension income, VA disability payments, and TSP withdrawals may trigger IRMAA surcharges on top of the standard Part B premium. IRMAA is based on modified adjusted gross income (MAGI) from two years prior.
| 2026 MAGI (Single) | 2026 MAGI (MFJ) | Monthly Part B Premium |
|---|---|---|
| $106,000 or less | $212,000 or less | $202.90 |
| $106,001 to $133,500 | $212,001 to $267,000 | $283.90 |
| $133,501 to $167,000 | $267,001 to $334,000 | $405.00 |
| $167,001 to $200,000 | $334,001 to $400,000 | $526.10 |
| Above $500,000 | Above $750,000 | $608.00 |
An O-6 retiree collecting a $70,000 pension, $40,000 in VA disability (tax-exempt but counted for IRMAA), and taking $50,000 in TSP distributions could easily land in the second or third IRMAA bracket.
The Checklist: What to Do Before 65
12 months before your 65th birthday:
- Confirm your Social Security work history (40 quarters) for automatic Part A eligibility at ssa.gov
- Estimate your MAGI for the year you turn 65 to anticipate IRMAA brackets
- Review any TSP withdrawal plans that could spike your income in the enrollment year
6 months before:
- Sign up for Medicare Part B through ssa.gov or your local Social Security office
- Confirm your DEERS enrollment is current through milConnect
3 months before:
- Verify Part B enrollment is processed
- Confirm TRICARE For Life activation (it should be automatic once Part A and Part B are active, but verify through your regional contractor)
Birthday month:
- Confirm TFL is active by calling the TFL contractor or checking your benefits status online
For a deeper look at how military pension income interacts with Virginia state taxes, see our guide to the Virginia $40,000 military retirement tax break. If you are comparing the TSP to a rollover IRA, our piece on what to do with your 401(k) when you leave a job covers the analysis. And for the broader retirement income picture, see how much should you have saved for retirement by age.
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