Medicare Enrollment Periods and Late Penalties

Medicare has several different enrollment windows, and missing the one that applies to you can mean a lifetime late penalty, not just a delay. This page covers every window and includes live calculators for the Part B and Part D late enrollment penalties.

By Victoria Cabrera — 20+ years in health insurance, focused on the Medicare market since 2015, NABIP speaker.

The enrollment windows, one by one

Initial Enrollment Period (IEP): a one-time 7-month window around your 65th birthday month. See the turning 65 timeline tool for your exact dates.
Annual Enrollment Period (AEP): October 15 to December 7 every year. Join, switch, or drop a Medicare Advantage or Part D plan for the following January 1.
Medicare Advantage Open Enrollment Period (MA OEP): January 1 to March 31 every year, for people already in a Medicare Advantage plan to make one switch.
Special Enrollment Period (SEP): triggered by a specific event, most commonly active employer coverage through current work (20+ employees), moving out of a plan's service area, or losing other coverage involuntarily.
General Enrollment Period (GEP): January 1 to March 31 every year, for people who missed their Initial Enrollment Period and have no SEP. Coverage starts the first day of the month after you sign up.
Medigap Open Enrollment Period: a one-time 6-month window starting the first day of the month you are 65+ and enrolled in Part B, with no medical underwriting.

Special Enrollment Periods: the employer-coverage exception

If you (or a spouse) are actively working at 65 with group health coverage from an employer with 20 or more employees, you can generally delay Part B without a penalty. Once that coverage or the employment ends, you get an 8-month Special Enrollment Period to sign up penalty-free. This is a different rule from VA coverage, which does not count as creditable coverage for Part B, see the Medicare & Veterans guide for that distinction. Employers with fewer than 20 employees follow different rules, where Medicare generally becomes primary at 65 regardless of continued work.

Part B late enrollment penalty calculator

Educational estimate only, using the 2026 standard Part B premium of $202.90. This penalty applies for as long as you have Part B, generally for life.

Enter a number of years above to see your estimated penalty.

Part D late enrollment penalty calculator

Educational estimate only, using the 2026 national base beneficiary premium of $38.99 (not what any specific plan charges, this base figure is only used to calculate the penalty). The penalty is added to whatever Part D plan premium you choose, for as long as you have Part D.

Enter a number of months above to see your estimated penalty.

Part A late penalty (only if you have to buy Part A)

Most people get Part A premium-free because they or a spouse paid Medicare taxes long enough. If you don't qualify for premium-free Part A and delay buying it, your premium increases 10%, and you pay that higher rate for twice the number of years you were eligible but did not enroll.

Worked example: the 2026 full Part A premium is $565/month. Someone eligible but unenrolled for 2 years owes a 10% penalty, $56.50 extra a month, paid for 4 years (twice the 2-year delay) before reverting to the standard premium.

Source: https://www.cms.gov/newsroom/fact-sheets/2026-medicare-parts-b-premiums-deductibles

Medigap Open Enrollment: a separate, one-time window

Your Medigap Open Enrollment Period is a one-time, 6-month window starting the first day of the month you are 65 or older and enrolled in Part B. During this window, any insurer that sells Medigap in your area must sell you any plan it offers at its best available rate, with no medical underwriting. After it closes, insurers can generally medically underwrite you, with a few federal and state exceptions, such as a "trial right" if you leave a Medicare Advantage plan within your first year on it. See the full Medicare Supplement guide for how these plans work.

Where to go next

Use the turning 65 timeline tool to find your personal Initial Enrollment Period dates. If you have VA or TRICARE coverage, read the Medicare & Veterans guide before you decide to delay any part of Medicare, VA coverage does not protect you from the Part B penalty the way real employer coverage does.

866-717-8683 Book a free review

Common questions about enrollment and penalties

When is my Initial Enrollment Period?

It is a 7-month window: 3 months before the month you turn 65, your birthday month, and 3 months after. Use the turning 65 timeline tool for your exact dates.

What is the Annual Enrollment Period and how is it different from my Initial Enrollment Period?

The Annual Enrollment Period, October 15 to December 7 every year, is for people already on Medicare to join, switch, or drop a Medicare Advantage or Part D plan for the following January 1. Your Initial Enrollment Period is a one-time, personal window around your 65th birthday.

I missed my Initial Enrollment Period and don’t have other coverage. What do I do?

You can sign up during the General Enrollment Period, January 1 to March 31 each year, with coverage starting the first day of the month after you sign up. A Part B late enrollment penalty will generally apply for as long as you have Part B.

I have coverage through my own or my spouse’s job. Do I still need to sign up at 65?

If the employer has 20 or more employees, you can generally delay Part B without a penalty until that coverage or the employment ends, then you get an 8-month Special Enrollment Period to sign up. If the employer has fewer than 20 employees, the rules are different, confirm with your employer’s benefits office before assuming you can wait.

What is the Medicare Advantage Open Enrollment Period?

January 1 to March 31 each year, for people already enrolled in a Medicare Advantage plan to make one switch, either to a different Medicare Advantage plan or back to Original Medicare with a Part D plan. It is not available to people who are not yet on a Medicare Advantage plan.

What is the Medigap Open Enrollment Period?

A one-time, 6-month window that starts the first day of the month you are 65 or older and enrolled in Part B. During it, insurers must sell you any Medigap plan they offer at their best available rate with no medical underwriting. After it closes, insurers can generally medically underwrite you.

How much is the Part B late enrollment penalty?

Generally 10% of the standard Part B premium for each full 12-month period you were eligible but did not enroll and did not have qualifying coverage, added to your premium for as long as you have Part B. Use the calculator on this page to estimate your own.

Sources

Figures verified 2026-10-01. No data you enter above is stored, saved, or sent anywhere; both calculators run in your browser only.