Excises are prorated on a monthly basis. If you register a motor vehicle after the beginning of any calendar year, no excise will be imposed for those months, if any, which have fully elapsed before the vehicle is registered. If a vehicle is registered for any part of a month, however, the excise will be due for all of that month. If you sell or trade a vehicle or move during the year, you should generally pay the full excise tax when billed to avoid any penalties. You should then contact the Assessors office to determine your eligibility for an abatement or refund and the documentation required.