{"id":23483,"date":"2026-11-03T23:34:21","date_gmt":"2026-11-03T23:34:21","guid":{"rendered":"https:\/\/www.youragecalculator.com\/blog\/medicare-enrollment-window-in-your-first-year\/"},"modified":"2026-11-03T23:34:21","modified_gmt":"2026-11-03T23:34:21","slug":"medicare-enrollment-window-in-your-first-year","status":"publish","type":"post","link":"https:\/\/www.youragecalculator.com\/blog\/medicare-enrollment-window-in-your-first-year\/","title":{"rendered":"Medicare Enrollment in Your First Year: Windows, Penalties, and the 20-Employee Test"},"content":{"rendered":"
\n

Turning 65 makes you eligible for Medicare, but eligibility and enrollment are two different events, and the gap between them is where people get charged more than they expect. The rules depend on whether you are already collecting Social Security, whether you are still on an employer plan, and how many people your employer covers. Here is how each situation actually plays out.<\/p>\n

If you are already drawing Social Security<\/h2>\n

You are auto-enrolled in both Part A and Part B to start on the first day of the month you turn 65. No application, no forms. Your Medicare card arrives roughly three months before your birthday.<\/p>\n

Part A is premium-free for most people who paid Medicare taxes for at least 40 quarters, which is ten years of work. Part B is not free \u2014 the 2026 standard premium is $185.00 per month, with the deductible at $257 and coinsurance at 20% of Medicare-approved amounts after that. That premium is deducted from your Social Security benefit automatically.<\/p>\n

There is one quiet trap here: if you are still working and covered by an employer plan, auto-enrollment will still happen. If you want to decline Part B, you must actively opt out by following the instructions on the form that comes with your card. If you miss that window, you keep paying the premium for coverage you may not need.<\/p>\n

If you are not yet drawing Social Security<\/h2>\n

You must sign up yourself, and the Initial Enrollment Period is the key structure: a seven-month window that begins three months before your 65th birthday month, includes it, and ends three months after. Sign up in the first three months and coverage starts on your birthday month. Sign up during your birthday month and it starts the following month. Sign up in the last three months and coverage can be delayed by one to three months \u2014 which, without other creditable coverage, means a gap.<\/p>\n

For a concrete example: a person born on 12 March reaches 65 in March 2026. Their Initial Enrollment Period runs from 1 December 2025 to 30 June 2026. Enrolling in December 2025 or January 2026 gives a 1 March 2026 start. Enrolling in May 2026 pushes the start to 1 June. Enrolling in June 2026 means a 1 July start \u2014 two months of coverage gap if nothing else covered them.<\/p>\n

Still working with employer coverage<\/h2>\n

This is where most confusion lives, and it turns on a single question: how many employees does the employer have?<\/p>\n\n\n\n\n\n\n\n\n
Your employer size<\/th>\nIs the employer plan primary at 65?<\/th>\nShould you take Part B now?<\/th>\n<\/tr>\n<\/thead>\n
20 or more employees<\/td>\nYes, employer plan pays first<\/td>\nUsually no \u2014 you qualify for a Special Enrollment Period later<\/td>\n<\/tr>\n
Fewer than 20 employees<\/td>\nNo, Medicare pays first<\/td>\nYes \u2014 enroll during your Initial Enrollment Period<\/td>\n<\/tr>\n
Self-employed with marketplace plan<\/td>\nNo<\/td>\nYes \u2014 marketplace coverage is not creditable<\/td>\n<\/tr>\n
COBRA coverage<\/td>\nNo<\/td>\nYes \u2014 COBRA is not creditable coverage<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The employer-size test only applies to coverage through your own current employment or a spouse’s current employment. Retiree plans, COBRA, and marketplace plans never count, no matter how good they are. If you decline Part B without creditable coverage, the late enrollment penalty is 10% of the standard premium for each full 12-month period you waited \u2014 and it is permanent.<\/p>\n

What “creditable coverage” actually means<\/h2>\n

For Part B, any group health coverage based on active employment counts. For Part D (prescription drugs), the test is different and stricter: the plan must be at least as good as Medicare’s standard drug coverage, and your plan must tell you in writing each year whether it qualifies. Retiree drug coverage from a former employer often does not qualify, which is why people who retire at 63 and keep retiree coverage frequently face a Part D penalty when they finally enroll.<\/p>\n

The Part D late penalty is 1% of the national base beneficiary premium for each month without creditable coverage. On the 2026 base premium of $36.78, twelve months without coverage means roughly $4.41 per month extra, added for as long as you have Part D.<\/p>\n

What it costs to get this wrong<\/h2>\n

Three realistic scenarios, same 65-year-old, different decisions:<\/p>\n