When is my MCS-150 biennial update due?
Every 24 months under 49 CFR §390.19, with the exact month keyed to your USDOT digit pattern. The second-to-last digit sets the month and the last digit sets odd/even-year cadence. FMCSA publishes a digit-to-month chart on the MCS-150 form and sends an email reminder if the carrier has a current contact email on file.
49 CFR §390.19(b)(1) requires every motor carrier with an active USDOT to file an MCS-150 update at least every 24 months. The cadence is staggered across carriers based on USDOT number to spread the workload across all months of the year.
The mapping: the second-to-last digit of the USDOT determines the month (1=Jan, 2=Feb, ... 9=Sep, 0=Oct), and the last digit determines whether the filing is due in odd-numbered or even-numbered years (odd last digit → odd year, even last digit → even year). So USDOT 12345 (last 5, second-to-last 4) is due in May of odd years.
FMCSA sends an email reminder to the carrier's registered contact roughly 90 days before the due date. Carriers with stale contact emails (a common failure mode for owner-operators who switched email providers) miss the reminder and slip into overdue status.
Filing is permitted any time during the due month. Filing earlier than the due month is not penalized — the next biennial cycle still runs from the original date pattern, not from the early-filed date. So filing 30 days early does not reset the clock.