You file an MCS-150 every other year. This biennial form serves as an update to the information associated with your USDOT number, and your DOT number will tell you when you need to file.
If the second-to-last digit of your DOT number is odd, you will file your MCS-150 every odd year (2023, 2025, 2027, etc.). Alternatively, if the second-to-last digit is even, you will file your MCS-150 in the even years (2024, 2026, 2028, etc.). The last digit of your DOT number represents the month in which you will need to file, with “0” representing the month of October.
Every other year is the requirement, but you may also refile your MCS-150 whenever you need to make changes to your USDOT.