Is there a penalty if I'm late signing up for Medicare?

Yes. If you aren’t covered by one of the exceptions listed below, you can be charged up to 10 percent more for Medicare Part B — the part of Medicare that provides standard medical insurance — for each full year past the eligibility age of 65 that you delay enrolling. (That is, 10 percent if you waited 12 months, 20 percent if you waited 24 months, and so on.)

The penalty is applied to your premiums permanently, and it adds up. Medicare Part A, which covers hospitalization, comes at no cost for most recipients, but Part B carries premiums. The base rate in 2025 is $185 a month. If you’re carrying a one-year late fee, you’ll pay an extra $222 for Part B in 2025 and bigger surcharges in future years as premiums rise.

Now for those exceptions. You can choose not to sign up for Part B at 65 without facing a late fee down the road if:

• You are still working and have group coverage through a company that employs at least 20 people. In this case, you can delay signing up for Part B until your employment ends. When that happens, you have eight months to sign up without incurring the penalty.
• Your spouse is working and you are covered through your spouse’s group insurance. Same rules as above.
• You have Part A coverage and are subsequently diagnosed with end-stage renal disease.

Keep in mind

• If you are already collecting Social Security benefits at 65, the Social Security Administration (SSA) will sign you up automatically for Medicare Parts A and B, but you can opt out of Part B. If you wish to do so, contact the SSA. 
• If you are not yet on Social Security, you have an initial window of seven months, sandwiched around your 65th birthday, to enroll in Medicare.