The program to calculate the road tax enables you to calculate the amount you have to pay during the period when payment is due (which coincides with the month following the expiry date).
If the calculation is done on a date after the period when payment is due, the service will also calculate any fine and interest due.
If, however, the calculation is made before the period of payment, the program will refer to the expiry of the previous year and indicate the increases due.
N.B. if the program indicates fines and interest, this does not necessarily imply that payments already made are irregular.
Road tax falls under the jurisdiction of the Regional authorities who are responsible for managing the data bases relating to payments made.