If there is WeekDays option set in monthly recurrence rule and try to get the occurence start the method just adds the interval to the start day, rather than considering the WeekDays option. CLOSED: Not an issue. The method is not intended to return real occurrence dates but rather dates that are potential occurrences and must be checked. The method is not correctly named but renaming it will result in a breaking change. The description of the method is updated. To achieve the desired functionality use OccurrenceEnumerator.