Medicare Enrollment Timeline

When do you actually have to sign up for Medicare, and what does it cost to be late? The deadlines cluster around your 65th birthday, and miss the wrong one and you can owe a higher premium for the rest of your life. The system rewards being early and punishes being late, so work the calendar deliberately.

Your initial enrollment period is a seven-month window: the three months before your 65th birthday month, the birthday month itself, and the three months after. Sign up in the first three months and coverage starts the month you turn 65. There’s an important exception. If you’re still working at a large employer with creditable group coverage, you may be able to delay Part B without penalty and enroll later through a special enrollment period. Confirm that your specific coverage qualifies before you rely on it, because the late penalty is permanent.

Three to six months before 65

• Decide whether you’re enrolling at 65 or delaying because of active large-employer coverage. If delaying, get written confirmation that your coverage is creditable.
• Choose your path: Original Medicare with a Medigap supplement and a separate drug plan, or a Medicare Advantage plan that bundles them. The parts A, B, C, and D breakdown explains the pieces.
• If you have a health savings account, stop contributions before Medicare starts, since you can’t contribute once enrolled.

The month around your 65th birthday

• Enroll in Part A and, unless you’re properly delaying, Part B during your initial enrollment window.
• Sign up for either a Medigap plan plus a Part D drug plan, or a Medicare Advantage plan.
• Coordinate dates with your spouse, since Medicare is individual and you won’t both qualify at the same time. See Spouse Medicare Enrollment Coordination.

After you enroll

• Confirm your premiums, and check whether the IRMAA surcharge applies based on your income from two years ago.
• If a major event like retirement dropped your income below the two-year-old figure Medicare used, file Form SSA-44 to ask for a lower premium based on your current income.
• Make sure the younger spouse has a coverage bridge in place if your enrollment ends a shared plan.

For higher-net-worth households

The premium tier you land in is driven by income you reported two years earlier, so Roth conversions and other big income events in the years before 65 quietly set what you pay at 65. The full mechanics are in IRMAA Two-Year Lookback Planning. Plan the enrollment dates and the income that sets the surcharge together, not separately.

Get the dates right and Medicare is a formality. Get them wrong and you pay for the slip every month for life. Mark the calendar early.