Field help (ENDPERDAT) 

This field displays the period end date which the due date is about. The end date of the first period must be entered. The end dates of the next periods are automatically defined as follows:
1/ If the period end date corresponds to the last day of a month, the end date of each of the following periods will correspond to the last day of a month.
2/ If the end date of the first period does not correspond to the last day of a month, each created period will terminate with the same day as the first period. Each created period will have the same number of months as the first period.