If you are already enrolled in a Medicare plan and don’t make any changes during open enrollment, your plan will automatically renew on January 1. If you are over 65 and haven’t enrolled in Medicare yet or missed your initial enrollment period, you have the opportunity to enroll during the general enrollment period from January 1 to March 31, and your coverage will start July 1. If you’re enrolling late, you may have to pay penalties. Here are some potential late enrollment penalties you might be faced with: Medicare Part A: If you don’t qualify for premium-free Medicare Part A and have to purchase it, your monthly premium will increase by 10%. The higher premium will apply for twice the number of years that you didn’t sign up. Medicare Part B: Your premiums will increase by 10% for each full 12-month period that you were late signing up for Medicare benefits. Medicare Part D: The penalty is calculated by multiplying 1% by the national base beneficiary premium by the number of months that you skipped prescription drug coverage. The amount is rounded up to the nearest $0.10.