In decision J 4/91 (OJ 1992, 402) the Legal Board of Appeal held that when calculating the six-month period for the payment of a renewal fee with additional fee under Art. 86(2) EPC 1973, R. 83(4) EPC 1973 should be applied mutatis mutandis in the light of R. 37(1), first sentence, EPC 1973. This meant that the six-month period did not end on the day of the subsequent sixth month corresponding "in number" to the due date according to R. 37(1), first sentence, EPC 1973 but on the day which was equivalent to this due date by virtue of its being the "last day of the month". For the purposes of calculating the additional period under Art. 86(2) EPC 1973, therefore, R. 83(4) EPC 1973, in the context of R. 37(1), first sentence, EPC 1973, resulted in a period running "from the last day of the month to the last day of the month".
The additional period started on the last day of the month specified in R. 37(1), first sentence, EPC 1973 even in the circumstances mentioned in R. 85(1), (2) and (4) EPC 1973. It followed that the occurrence of such circumstances at the beginning of the period did not result in the end of the period being postponed beyond the end of the sixth month and into the seventh month.