Can I correct my UCR fleet count after filing?
It depends on what went wrong. If the filing you already made reported the wrong count for the year - a miscount, or a number backed by neither your MCS-150 nor your actual prior-year count - that is a correction: go back through your base state's UCR office or the filer who submitted it, give the right count, and pay the difference if the correct bracket is higher. If your fleet simply changed after you filed, nothing is due: the UCR Plan's FAQ says a carrier is not required to file a supplemental report or fee when its fleet grows or shrinks during the registration year.
Your UCR bracket comes from a backward-looking count, not a live one. Under 49 USC §14504a(f)(3) it is the number of commercial motor vehicles on your most recently filed MCS-150 or, at your election, the number you owned or operated in the 12 months ending June 30 of the year before the registration year. The brackets are: Tier 1 (0-2 vehicles), Tier 2 (3-5), Tier 3 (6-20), Tier 4 (21-100), Tier 5 (101-1,000), Tier 6 (1,001+). The fee scales sharply across tiers - Tier 1 is $55 while Tier 6 is $54,165 for 2027.
A correction applies when the filing itself was wrong for that count - you keyed 4 vehicles when the MCS-150 said 8, for example. Contact your base state's UCR office or the filer who submitted the registration, give the right count and the basis for it, and pay the difference if the correct bracket is higher. Moving to a lower bracket is possible but expect to document it (vehicle registrations, IRP fleet schedules, lease records), because bracket retreats are what state auditors look at first.
Fleet growth after filing is different. The UCR Plan's FAQ answers it directly: a carrier subject to UCR fees is not required to file a supplemental report and fees if the size of its fleet increases or decreases during the year, because fees are set from the vehicle count for the preceding year and changes during the registration year are not reflected until the following year. A carrier that filed correctly at 18 power units (Tier 3) and grew to 22 mid-year does not owe a Tier 4 top-up for the current year - the 22 shows up in next year's count.
The practical risk runs the other way: the National Registration System pre-fills your renewal from the last MCS-150 on file with FMCSA, so an out-of-date MCS-150 gives you the wrong default count in one direction or the other. Keep the MCS-150 current through Motus and read the count before you pay. Our guide on how to update your UCR fleet size walks through the year-by-year mechanics.