Medicare.gov hosts current Medicare Premiums and a complete summary of Medicare Part A, B, and D penalties is maintained by the National Council on Aging. Part A penalties are rare, but there are Part B and D premium penalties you need to be aware of. Most noteworthy is the fact that late enrollment penalties are typically added to every monthly payment for the duration of your Medicare coverage.
For each 12-month period you delay enrollment in Part B, you will have to pay a 10% premium penalty, unless you have insurance based on your spouse's current work (job-based insurance) or are eligible for a Medicare Savings Program (MSP).
This penalty is permanently added to your Medicare drug coverage premium. You may owe a late enrollment penalty if there is a period of 63 or more days in a row when you do not have Medicare drug coverage or other creditable coverage.
Make sure you enroll during your Initial Enrollment Period. If you qualify for a Special Enrollment Period, make sure your employer coverage is creditable for Parts B and D and always have written proof of your prescription drug coverage.