I have a client who is being charged the irmaa for Medicare part B. He asked me when it will change, since his income from 2021 should put him into the lowest premium bracket for 2023. Does the irrma for part B change on the first day of the month that is 2 years prior to to their part B effective date? Or does is change for everyone based on a calendar year? He's looking for a specific date, and I've never heard of one. I've only heard that the premium for part B is based on the modified adjusted gross income from 2 years ago. Any help on narrowing that down to a specific date would really be appreciated!