Under Art. 8, first sentence, RFees (formerly Art. 9, first sentence, RFees 1973), a time limit for payment is in principle deemed to have been observed only if the full amount of the fee has been paid in due time. However, the EPO is given the discretion, where this is considered justified, to overlook any small amounts lacking without prejudice to the rights of the person making the payment (Art. 8, fourth sentence, RFees, formerly Art. 9, fourth sentence, RFees 1973).
The justification for overlooking a small fee underpayment has been considered by the boards of appeal in several cases. In T 130/82 (OJ 1984, 172) the board decided that it was justified to overlook an underpayment of just over 10%. In J 11/85 (OJ 1986, 1) the board stated that an underpayment of about 10% may as a rule be considered as a small amount (see also T 109/86 of 20.7.1987). See also T 343/02, where the underpayment of less than 2% due to the unexpected deduction of bank charges was overlooked.
In T 290/90 (OJ 1992, 368) the board found that this question must be decided on an objective basis, having regard to all the relevant circumstances of the case, and not on a subjective basis. It held that in the circumstances of that case 20% of the opposition fee could properly be regarded as a small amount, because it was inappropriate to punish the appellant for contending he was entitled to a reduction in the opposition fee (under R. 6(3) EPC 1973) and the missing 20% was paid soon after expiry of the period.
However, in T 905/90 (OJ 1994, 306, Corr. 556) the board found that the meaning of 'smallness' could best be determined by comparing the amount of shortfall with the amount of the full fee. A difference of 20% clearly could thus not, on purely arithmetical grounds, be regarded as small. It was with very small or trifling amounts that the former Art. 9 RFees 1973 (see now Art. 8 RFees) was designed to deal so as to prevent a loss of rights where an inadvertent error of some kind had led to a slight underpayment of an amount due in respect of the relevant proceedings.
In J 27/92 (OJ 1995, 288) the examination fee was underpaid by about 20%, amounting to DEM 560. Distinguishing T 905/90, the board defined the concept of a "small amount lacking" in the then Art. 9 RFees (see now Art. 8 RFees) as a fixed proportion of the amount of the particular fees to be paid. At most, 20% of the fee to be paid might be regarded as small within the meaning of the said provision. Moreover, the choice of 20% as the percentage to be considered a "small amount" would achieve the desirable end of making it possible to apply the former Art. 9 RFees (see now Art. 8 RFees) to cases where a party paying fees mistakenly sought to take advantage of the 20% reduction in fees available in relation to Art. 14(2) and (4) EPC 1973 under R. 6(3) EPC 1973 and the former Art. 12(1) RFees (see now Art. 14(1) RFees). In the case in point the board decided that it was justified to overlook the deficit as the applicant not only paid it without delay, but also appeared to have been misled into paying only 80% of the fees as a result of information provided by the EPO. For a different approach, see T 642/12.