Your Medicare Sign-Up Window Is 7 Months Wide. Use the Wrong Half and Coverage Comes Late

A 64-year-old in Ohio plans to call Social Security “sometime around her birthday” to sign up for Medicare. Her birthday is in August. If she enrolls during May, June, or July, her Part B coverage will begin August 1, the first day of her birthday month. If she waits until August to enroll, coverage will not begin until September 1. If she waits until November, the final month of her Initial Enrollment Period, coverage will not begin until December 1. The enrollment window remains open, but every month she waits after her birthday month pushes her coverage start date further into the future.

This article is for anyone approaching age 65 who has not yet enrolled in Medicare Part B. The Initial Enrollment Period is generous, but where you enroll within that seven-month window affects when coverage actually starts. The result is not a penalty. It is a potential gap in coverage.

The 7-Month Window Has Two Halves That Behave Differently

The IEP runs seven months: the three months before your 65th-birthday month, the birthday month itself, and the three months after. Coverage always starts on the first of a month. Where you sign up inside that window decides which first of the month that is.

Under the rule in effect for 2026, Part B (and premium Part A, if you owe one) starts like this:

• Sign up in any of the three months before your birthday month: coverage starts the first day of your birthday month.
• Sign up during your birthday month or any of the three months after: coverage starts the first of the month after you sign up.

Sign up early, and you are covered the day you turn 65. Sign up later in the same window, and every month you delay pushes the start date out by one more month. The window costs you uncovered time instead of charging a fine.

The Old Three-Month Delay Is Gone. The Gap Remains.

The enrollment rules are more forgiving than they used to be. Before January 1, 2023, someone who enrolled late in their Initial Enrollment Period could wait as long as three months for coverage to begin. Today, coverage generally starts the month after enrollment. That change shortened the delay, but it did not eliminate it. A beneficiary who enrolls during their birthday month will typically see coverage begin the following month. Someone who waits until the final month of the Initial Enrollment Period can still spend several months after turning 65 without Medicare coverage in place.

The Part B late-enrollment penalty is a separate issue entirely. The penalty does not apply during the Initial Enrollment Period. Instead, it generally begins only after that enrollment window closes. A beneficiary who signs up in the final month of the Initial Enrollment Period owes no penalty, even if coverage starts later than expected. The risk is not a surcharge. The risk is being without Medicare coverage during the months between turning 65 and the eventual coverage start date.

What the Gap Actually Costs

Use the 2026 standard Part B premium of $202.90 per month as the reference. The dollars you do not pay during an uncovered month look like savings, but they leave you exposed to the full cost of any care. A single in-network knee MRI runs four figures. A trip to the ER for chest pain runs five. COBRA, if available, often costs more than Part B and does not coordinate with Medicare once your IEP opens.

The action is one sentence: sign up in the first three months of your IEP. Coverage starts on your 65th birthday month, you pay the same premium you would have paid anyway, and there is no gap to insure around.

Do Not Confuse the IEP With the Other Windows

The IEP is one-time and tied to your birthday. Two other windows exist:

• General Enrollment Period (GEP): January 1 to March 31 each year, for people who missed the IEP and have no Special Enrollment Period. Coverage starts the month after you sign up, and you typically owe the late enrollment penalty.
• Special Enrollment Period (SEP): an eight-month window after employer coverage from current active employment ends. COBRA and retiree coverage do not qualify. Readers losing job-based coverage at 65 use this, not the IEP, but the IEP timing rule above still applies if they sign up before leaving the job.

What to Do

1. Mark the first day of the month three months before your 65th birthday. That is the day your IEP opens and the day to enroll at ssa.gov/medicare.
2. If you are still on active-employment group coverage at 65 and plan to keep working, confirm in writing that the plan is creditable for Part D and that your employer has 20 or more employees. Then decide whether to enroll in Part A only or both parts.
3. If your birthday month has already arrived and you have not enrolled, sign up this week. Each additional calendar month you wait inside the IEP adds another month of uncovered time on the back end.

Source note: Coverage start rules and the 2026 Part B standard premium are drawn from CMS and Medicare.gov guidance for the 2026 plan year.